Follow-up from "Show participants as well in assignees widget"

The following discussion from !145901 (merged) should be addressed:

• @ntepluhina started a discussion: (+1 comment)

  question: do I understand correctly that we're "caching" all the previous query responses in the component? Wondering whether this can be done with Apollo cache (most likely will require some digging on keyArgs). Not blocking for the current MR but maybe a good follow-up material