fix(installer): resolve feature selection in Agent installer

[thenextman]

Resolve issues with feature selection in the Agent installer.

First; I created a defined "Agent" feature instead of the existing default "Complete" feature. I made this mandatory for installation; it should not be possible to install the product without installing Devolutions Agent.

Second; a treeview was used for feature selection but is horribly buggy. Clicks were often not registered, or registered as double clicks, which would cause the visual state of the checkbox to be out of sync with it's actual state 😒 This often lead me to get the wrong features installed. It's not clear if this is because of underlying .NET Framework issues (this is a notorious control) or the mitigations built on top by WixSharp).

Since a treeview is only used to support feature hierarchies - which we don't use - I swapped it for a list view control and was able to vastly simplify the logic.

Finally, I added placeholder localization for the feature information and removed some code from the Gateway installer that was not being used here. I also corrected the feature assignment of the PEDM Desktop application.

[github-actions]

Let maintainers know that an action is required on their side

• Add the label release-required Please cut a new release (Devolutions Gateway, Devolutions Agent, Jetsocat, PowerShell module) when you request a maintainer to cut a new release (Devolutions Gateway, Devolutions Agent, Jetsocat, PowerShell module)

• Add the label release-blocker Follow-up is required before cutting a new release if a follow-up is required before cutting a new release

• Add the label publish-required Please publish libraries (`Devolutions.Gateway.Utils`, OpenAPI clients, etc) when you request a maintainer to publish libraries (Devolutions.Gateway.Utils, OpenAPI clients, etc.)

• Add the label publish-blocker Follow-up is required before publishing libraries if a follow-up is required before publishing libraries