ui: degrade gracefully when regions aren't known

[matthewtodd]

Part of #89949

Previously, when a tenant SQL instance had spun down (leaving us no way to remember which region it had been in), the SQL Activity pages would claim that statements and transactions had occurred in an "undefined" region.

This change moves from saying "undefined" to saying nothing at all, a slightly nicer user experience.

This broader problem of losing the region mapping has been described in #93268; we'll begin addressing it shortly.

Release note: None

[cockroach-teamcity]

This change is 

[matthewtodd]

Here are some screenshots from before this fix. Note the "undefined"s and the trailing commas.

[matthewtodd]

Bazel Extended CI failures are unrelated, fallout from #93754, fixed in #94005.

[19:50:50][Bench //pkg/sql/opt/partialidx:partialidx_test] --- FAIL: BenchmarkImplicator
[19:50:50][Bench //pkg/sql/opt/partialidx:partialidx_test]     implicator_test.go:284: unexpected error while building filters: invalid syntax @5
[19:50:50][Bench //pkg/sql/opt/partialidx:partialidx_test] FAIL
[19:50:50][Bench //pkg/sql/opt/partialidx:partialidx_test] I221220 19:50:50.475685 1 (gostd) testmain.go:80  [-] 1  Test //pkg/sql/opt/partialidx:partialidx_test exited with error code 1
[19:50:51][Bench //pkg/sql/opt/partialidx:partialidx_test] Process exited with code 1

[maryliag]

any way to remove the value so there is no , on the column, without any values after the , ?

Reviewed 6 of 6 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @matthewtodd)

[matthewtodd]

Yes! Sorry I wasn't clear. That's what this PR does, remove the comma. (The screenshots are of the Before Times.)

Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @matthewtodd)

[maryliag]

Ah cool!

Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @matthewtodd)

[matthewtodd]

Thanks, @maryliag!

bors r+

[craig]

Build succeeded:

• Bazel Essential CI (Cockroach)