kv/bulk: send ssts with lower admission control priority

[dt]

small refactor while I'm here since plumbing args to/from the kv.DB "helpers" has been a source of toil and merge conflicts lately.

Jira issue: CRDB-14737
Epic CRDB-2264

[cockroach-teamcity]

This change is 

[dt]

first two commits are #79086, ignore them here.

[erikgrinaker]

The detour through the kv.DB wrapper was just adding more plumbing, signatures, etc
to update to get an argument or return value through. Perhaps we should remove them
in a follow-up as this is the only non-test caller.

Agreed, I find the non-trivial DB helpers to mostly be a hassle. Should make it easy to construct and send requests instead.

[dt]

I'm a little wary about back-porting this so last minute, particularly given how much recent ingestion performance work we've been doing, so hopefully we can get it in asap so it has at least a few betas in which to bake.

[erikgrinaker]

I'm a little wary about back-porting this so last minute, particularly given how much recent ingestion performance work we've been doing, so hopefully we can get it in asap so it has at least a few betas in which to bake.

I'm fine with merging this as-is.

[dt]

I'm fine with merging this as-is.

👍 was just waiting on the open questions in #79086.

[sumeerbhola]

for the admission control bits

Reviewed 1 of 1 files at r2, 1 of 1 files at r3, 1 of 2 files at r4, all commit messages.
Reviewable status: complete! 1 of 0 LGTMs obtained (waiting on @stevendanna)

[dt]

TFTRs!

bors r+

[craig]

Build failed (retrying...):

• GitHub CI (Cockroach)

[craig]

Build succeeded:

• GitHub 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.

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error creating merge commit from ef29359 to blathers/backport-release-21.2-79126: 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 21.2.x failed. See errors above.

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[irfansharif]

blathers backport 21.2

[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 ef29359 to blathers/backport-release-21.2-79126: 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 21.2 failed. See errors above.

---

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