Add docs for user-installed apps (#6723)

add user install docs + new pages for interactions and overview of apps

docs/Change_Log.md

@@ -1,5 +1,42 @@
 # Change Log
 
+## User-Installable Apps Preview
+
+#### March 18, 2024
+
+> preview
+> User-installable apps are currently in preview. During the preview, there are major [limitations and known bugs](#DOCS_CHANGE_LOG/march-18-2024-limitations-and-known-issues), and API details are subject to change.
+
+Apps can now be installed to users—making them easier to install, discover, and access across Discord. User-installed apps can be used across all of a user's servers, within their (G)DMs, and in DMs with the app's bot user.
+
+When creating or updating your app, you can choose which installation types your app supports on the **Installation** page in your [app's settings](https://discord.com/developers/applications). To quickly get started, you can follow the new [Developing a User-Installable App tutorial](#DOCS_TUTORIALS_DEVELOPING_A_USER_INSTALLABLE_APP) or read details about the new changes below.
+
+This change introduces new concepts and fields across the API that apps will now encounter—
+
+###### API Changes
+
+**Concepts:**
+- [Installation context](#DOCS_RESOURCES_APPLICATION/installation-context) defines how an app was installed: to a user, a guild (server), or both. Currently, apps will default to only support the guild installation context, but the default may change in the future.
+- Commands can also support one or both installation contexts, with the default being the same as the app's supported installation context(s) at the time of command creation.
+- [Interaction context](#DOCS_INTERACTIONS_APPLICATION_COMMANDS/interaction-contexts) defines where a command can be used in Discord—within guilds, DM with your app's bot user, and/or within group DMs and DMs other than with your app's bot user.
+- The installation flow for apps have been updated so users can select whether they want to install an app to their account or to a server. 
+
+**API Fields:**
+- New `integration_types_config` field for [Applications](#DOCS_RESOURCES_APPLICATION/application-object) include the default scopes and permissions for app's supported installation contexts
+- New `integration_types` and `contexts` fields for [Commands](#DOCS_INTERACTIONS_APPLICATION_COMMANDS/application-command-object-application-command-structure) are the supported [installation](#DOCS_INTERACTIONS_APPLICATION_COMMANDS/installation-context) and [interaction](#DOCS_INTERACTIONS_APPLICATION_COMMANDS/interaction-contexts) contexts (respectively) for the command. Read [command contexts](#DOCS_INTERACTIONS_APPLICATION_COMMANDS/contexts) documentation for details.
+- New `context` field for [Interactions](#DOCS_INTERACTIONS_RECEIVING_AND_RESPONDING/interaction-object-interaction-structure) indicates the [interaction context](#DOCS_INTERACTIONS_APPLICATION_COMMANDS/interaction-contexts) where an interaction was triggered from.
+- New `authorizing_integration_owners` field for [Interactions](#DOCS_INTERACTIONS_RECEIVING_AND_RESPONDING/interaction-object-interaction-structure) includes a mapping of installation contexts that the interaction was authorized for, to related snowflakes for that context. Read [Authorizing Integration Owners Object](#DOCS_INTERACTIONS_RECEIVING_AND_RESPONDING/interaction-object-authorizing-integration-owners-object) for details.
+- `app_permissions` is now always serialized for interactions to indicate what [permissions](#DOCS_TOPICS_PERMISSIONS/permissions-bitwise-permission-flags) your app has access to in the context its' responding. For (G)DMs with other users, it will include the `ATTACH_FILES | EMBED_LINKS | MENTION_EVERYONE`, and for DMs with the app's bot user it will also contain `USE_EXTERNAL_EMOJIS` for the bot’s DM
+- New `interaction_metadata` on [Messages](#DOCS_RESOURCES_CHANNEL/message-object) that are created as part of an interaction response (either a response or follow-up). See [Message Interaction Metadata Object](#DOCS_RESOURCES_CHANNEL/message-interaction-metadata-object) for details.
+- `dm_permission` field for [Commands](#DOCS_INTERACTIONS_APPLICATION_COMMANDS/application-command-object-application-command-structure) is deprecated. Apps should use `contexts` instead.
+- `interaction` field for [Messages](#DOCS_RESOURCES_CHANNEL/message-object) is deprecated. Apps should use `interaction_metadata` instead.
+
+###### Limitations and Known Issues
+
+- During the preview, interaction responses for the user installation context will be forced to be ephemeral in servers with over 25  members. Forced ephemerality is enforced at the client-level, so your app does not need to manually pay attention to server size, and will not receive errors via the API.
+- All [follow-up messages](#DOCS_INTERACTIONS_RECEIVING_AND_RESPONDING/followup-messages) are currently forced to be ephemeral in DMs
+- Follow-up messages have a bug where they will not correctly respect user permissions
+
 ## Discord Activities: Developer Preview of the Embedded App SDK
 
 #### March 18, 2024

docs/best_practices/Crafting_your_App_Directory_Product_Page.md

@@ -3,7 +3,7 @@
 So you’ve made an app on Discord and are ready to opt in to discovery on the App Directory! Or maybe you have already listed your app but aren’t seeing as much traction to it as you’d like? Whatever stage you’re at, this guide has some tips and tricks from your friendly Discord Staff members to help boost performance of your App Directory Product Page.
 
 > info
-> This guide references settings and information you can set up and modify within your [app's settings](https://discord.com/developers/applications). If you don't have an app yet, you can follow the [Getting Started guide](#DOCS_GETTING_STARTED).
+> This guide references settings and information you can set up and modify within your [app's settings](https://discord.com/developers/applications). If you don't have an app yet, you can follow the [Getting Started guide](#DOCS_QUICK_START_GETTING_STARTED).
 
 ## The Elevator Pitch: Quickly tell your users what your app does