[Drilldowns] URL Drilldown extension points

[Dosant]

Part of: #55324

Describe the feature:

To make URL drilldown use full outside of dashboard we need to introduce following extension points:

• Extension point for context.$ variables (allows to decouple from embeddable and add info about dashboard or canvas) More here
• Extension point for supported triggers More here
• Extension points for handlebars helpers

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[ppisljar]

Thank you for contributing to this issue, however, we are closing this issue due to inactivity as part of a backlog grooming effort. If you believe this feature/bug should still be considered, please reopen with a comment.