allows plugins to define validation schema for "enabled" flag

[mshustov]

Summary

the first commit closes: #49012
validation error message gives a hint about source of the error: "[config validation of [key]]:...

the second commit closes: #49289
plugins are able to define config schema with default value for enabled flag

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

• [ ] This was checked for cross-browser compatibility, including a check against IE11
• [ ] Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• [ ] Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
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For maintainers

• This was checked for breaking API changes and was labeled appropriately
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Dev docs

If you want your plugin to be disabled by default you can specify it via config:

export const config = {
  schema: schema.object({ enabled: schema.boolean({ defaultValue: true }) })
}

[elasticmachine]

Pinging @elastic/kibana-platform (Team:Platform)

[mshustov]

As an alternative solution, we can always extend the plugin config with a schema for the enabled flag. Although, I'd prefer to do not touch the user schema.

[elasticmachine]

💔 Build Failed

• continuous-integration/kibana-ci/pull-request
• Commit: 910c9d9

[paul-tavares]

Hi @restrry
I tried this out for the Endpoint Security plugin and it works well - thank you for working on it.
Do you know where I can find more information about config (what's available and how to use it)?

[mshustov]

@paul-tavares right now you can only specify config schema. More details about config https://github.com/restrry/kibana/blob/b9a43a1788486c0d064cbe7aaff1fc7e987f7dfa/src/core/MIGRATION.md#configure-plugin
A schema is defined with @kbn/config-schema package. Docs for the package are in progress #50307
Let me know if you see something missed in the docs.

[mshustov]

@elasticmachine merge upstream

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 4a307f2

[paul-tavares]

@restrry thanks for that. I would not have thought of looking in the Migration docs because we're a brand new plugin that will be using only the new platform - but we're probably the exception. I will make a mental note to also review migration type of docs when looking for info. 😄

Re: Docs
I did not see an area that detail what configuration attributes are available from the platform side - for example: enabled. Knowing that list would help to ensure that plugins don't try to use "reserved" settings. The example does provide some other values, but not clear if those are used by the platform or if specific to the plugin.

One observation I would like to share, which perhaps is more specific to the disablement of a plugin, is the config is added to the server/index, which causes the actual sever code to be loaded (require()). Although the exported plugin function is never called, depending on what the plugin server code does that might acutely cause it to "run" (example: any type of setup outside of Plugin setup, start and stop lifecycle hooks)

[mshustov]

@elasticmachine merge upstream

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 3836c06