Add OR filtering for assignees on group/project issues list

What does this MR do and why?

This MR adds OR filtering for assignees on the group/project issues list

• When the or_issuable_queries feature flag is enabled:
  • User can perform OR filtering for assignees
  • The operators are shown with friendly text (e.g. is)
• When the or_issuable_queries feature flag is disabled:
  • User cannot perform OR filtering for assignees
  • The operators are shown as symbols (e.g. =)

No changelog required as it is behind the feature flag or_issuable_queries, defaulted off

Issue: #23532 (closed)

Screenshots or screen recordings

Screen_Recording_2022-11-07_at_2.25.36_pm

How to set up and validate locally

1. In rails console enable the feature flag

   Feature.enable(:or_issuable_queries)

2. Visit any group or project issues list pages such as http://127.0.0.1:3000/h5bp/html5-boilerplate/-/issues/
3. Test OR filtering in the filtered search bar

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #23532 (closed)