release-25.4: metric: add labels for sql.*.started.count

[blathers-crl]

Backport 1/1 commits from #151946 on behalf of @ZhouXing19.

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Previously, only metrics for executed SELECT|UPDATE|DELETE|INSERT statements are labeled, while their started equivalent are not labeled. This commit is to label these metrics. Since they are not frequently used metrics, they are not marked as Essential.

Fixes: #152074

Release note (ops change): sql.select.started.count, sql.insert.started.count, sql.update.started.count, sql.delete.started.count are now labeled with sql.started.count.

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Release justification: low-risk improvement to observability.

[blathers-crl]

Thanks for opening a backport.

Before merging, please confirm that the change does not break backwards compatibility and otherwise complies with the backport policy. Include a brief release justification in the PR description explaining why the backport is appropriate. All backports must be reviewed by the TL for the owning area. While the stricter LTS policy does not yet apply, please exercise judgment and consider gating non-critical changes behind a disabled-by-default feature flag when appropriate.

[blathers-crl]

It looks like your PR touches production code but doesn't add or edit any test code. Did you consider adding tests to your PR?

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

[cockroach-teamcity]

This change is 

[yuzefovich]

@yuzefovich reviewed 2 of 2 files at r1, all commit messages.
Reviewable status: complete! 0 of 0 LGTMs obtained (waiting on @dhartunian and @ZhouXing19)

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-- commits line 12 at r1:
nit: leftover.

[dhartunian]

Release Justification: low-risk configuration change to metric naming. New endpoint with labels does not have stable API yet.