[POC] Dashboard filter by user

[Dosant]

Summary

Part of https://github.com/elastic/kibana-team/issues/769

This is a poc for adding filters by author on the dashboard listing page.

Here is the demo:

poc.filter.by.user.mov

I'll write up a doc to discuss the poc and the implementation.

In this POC:

• added created_by to the base saved object interface.
• created_by is passed as a CreateOptions from outside, but with adding security apis to core, in the actual implementation core could take care of populating it from inside [Security into Core] expose authc.getCurrentUser from core.security #177976
• user filter UI uses existing UserProfilesPopover component 👍
• the POC is using security.userProfiles.suggest to show the list of users (not only the ones that have a dashboard 👎)
• The username from the search query is using security.userProfiles.suggest to look up the user id to execute the search