[Discover] Standardize extension point actions

[davismcphee]

Summary

This PR standardizes how actions that affect Discover state are passed to extension points within an actions object to make it clearer and more consistent for consumers. I also think it would be a good idea to check whether a specific action is available to determine if it can be used vs relying on separate props (e.g. isDocViewerEnabled).

Checklist

• 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
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This was checked for breaking HTTP API changes, and any breaking changes have been approved by the breaking-change committee. The release_note:breaking label should be applied in these situations.
• Flaky Test Runner was used on any tests changed
• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines
• Review the backport guidelines and apply applicable backport:* labels.

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 7063685

Metrics [docs]

Async chunks

Total size of all lazy-loaded chunks that will be downloaded as the user navigates the app

id	before	after	diff
discover	1.1MB	1.1MB	+4.0B

History

• 💚 Build #315971 succeeded c9e73ab

cc @davismcphee