ISSUE-13807: Ability to store metadata about functions

[sijie]

Original Issue: apache#13807

---

would be very handy to have the ability to store metadata about functions

analogous to metadata for topics

apache#12629

advantages (same as for topics):

Introduce the ability to store metadata about topics.
This would be very useful as with metadata you could add labels and other
pieces of information that would allow defining the purpose of a topic,
custom application-level properties.
This feature will allow application-level diagnostic tools and maintenance
tools to not need external databases to store such metadata.

Imagine that we could add a simple key value map (String keys and String
values) to the topic.
These metadata could be set during topic creation and also updated.

[github-actions]

The issue had no activity for 30 days, mark with Stale label.