Add Search Applications API

[carlosdelest]

Add Search Applications API, including both CRUD and _search request.

Reopening this from #2080, as Github actions need the PR to be done from the same repo

[github-actions]

Following you can find the validation results for the APIs you have changed.

API	Status	Request	Response
search_application.delete_behavioral_analytics	🟠	Missing type	Missing type
search_application.delete	⚪	Missing test	Missing test
search_application.get_behavioral_analytics	🟠	Missing type	Missing type
search_application.get	⚪	Missing test	Missing test
search_application.list	⚪	Missing test	Missing test
search_application.post_behavioral_analytics_event	🟠	Missing type	Missing type
search_application.put_behavioral_analytics	🟠	Missing type	Missing type
search_application.put	⚪	Missing test	Missing test
search_application.search	⚪	Missing test	Missing test

You can validate these APIs yourself by using the make validate target.

[kderusso]

Looks great so far, a couple comments! 💯

[kderusso]

It looks like we may need to update the stability here to experimental as well?

[kderusso]

I think we need to update these @stability tags too

[sethmlarson]

This looks good to me!

@kderusso We'll eventually need to update the stability tags, but I was thinking we could get this PR merged and then I'll manually resync the rest-api-spec stubs before fixing the stabilities. Otherwise we need to resync, rebase, and all that, might be easier this way?

[carlosdelest]

@kderusso , as @sethmlarson said, this can be done in a separate PR with the syncs already done. I'm merging this PR and we'll take care of that in a separate one 👍