Apply /remind_me to work items

This is available on legacy issues and MRs, but we need to add it to work items at both the project and group level.

Original description when focus was on adding to legacy Epics:

The only reason we didn't allow this feature on Epics as part of the PoC was that the feature flag was shipped with project as the actor. If we change this to group instead, we can apply this to Epics. This will require us to move the code into the issuables quick action definition file as well as adding another table (remind_me_epics) which can be done as part of #459899