sql: explain create function op

[rharding6373]

EXPLAIN CREATE FUNCTION ... now emits some output instead of failing.

Fixes #96046

Epic: none
Release note: none

[cockroach-teamcity]

This change is 

[msirek]

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @mgartner)

[mgartner]

Thanks for fixing this!

Let's backport this to 22.2. I've added the label.

Reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 2 of 0 LGTMs obtained (waiting on @rharding6373)

[rharding6373]

TFTRs! And for adding the backport label.

bors r=msirek,mgartner

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)

[blathers-crl]

Encountered an error creating backports. Some common things that can go wrong:

1. The backport branch might have already existed.
2. There was a merge conflict.
3. The backport branch contained merge commits.

You might need to create your backport manually using the backport tool.

---

error creating merge commit from 85cf1dc to blathers/backport-release-22.2-96253: POST https://api.github.com/repos/cockroachdb/cockroach/merges: 409 Merge conflict []

you may need to manually resolve merge conflicts with the backport tool.

Backport to branch 22.2.x failed. See errors above.

---

_{🦉 Hoot! I am a Blathers, a bot for CockroachDB. My owner is dev-inf.}