WIP POC: Ss/realtime 2

What does this MR do?

POC for real time on in issuable sidebar Just on Issues Page

Something that has come up is when the assignees is updated in real time, the assignees dropdown in the issue sidebar, the checked assignees are out of date. I believe this is due to to the logic in user_select and on load of the issue board_sidebar_user_data is called to populate the data with the correct data and fields(not being reactive).

Todo:

• Feature Flag guard
• Figure out how to make the assignees dropdown respond correctly to real time.
• Revise after final pass on parent MR.
• Specs

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team