release-21.2: release-22.1: gcp,s3,azure: make the storage client upload chunk size configurable

[blathers-crl]

Backport 1/1 commits from #80947 on behalf of @blathers-crl[bot].

/cc @cockroachdb/release

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Backport 1/1 commits from #80668 on behalf of @adityamaru.

/cc @cockroachdb/release

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This change adds a cloudstorage.write_chunk_size cluster setting
that allows us to control the size of the chunks buffered by the
cloud storage client when uploading a file to storage. The setting defaults to
8MiB.

Prior to this change gcs used a 16MB buffer, s3 a 5MB buffer, and azure a 4MB
buffer. A follow up change will add memory monitoring to each external storage
writer to account for these buffered chunks during upload.

This change was motivated by the fact that in google-cloud-storage
SDK versions prior to v1.21.0 every chunk is given a hardcoded
timeout of 32s to successfully upload to storage. This includes retries
due to transient errors. If any chunk during a backup were to hit this
timeout the entire backup would fail. We have additional work to do
to make the job more resilient to such failures, but dropping the default
chunk size might mean we see fewer chunks hit their timeouts.

Release note: None

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Release justification: low risk, high benefit change that reduces the chances of a backup failing because of chunk retry timeouts in the cloud storage sdk

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Release justification:

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[msbutler]

friendly ping! should we merge this?

[github-actions]

Reminder: it has been 3 weeks please merge or close your backport!