Add UI for subscribed filter

What does this MR do and why?

This implements the UI for Allow Filtering by subscribed issues in the gra... (!134807)

Related to List of all subscribed issues (#14972)

Screenshots or screen recordings

How to set up and validate locally

1. Feature.enable(:filter_subscriptions)

2. Check the search tokens in the issue lists (project, group, dashboard)

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.