Rename S3 scrubber to storage scrubber

[arpad-m]

The S3 scrubber contains "S3" in its name, but we want to make it generic in terms of which storage is used (#7547). Therefore, rename it to "storage scrubber", following the naming scheme of already existing components "storage broker" and "storage controller".

Part of #7547

[github-actions]

3198 tests run: 3056 passed, 0 failed, 142 skipped (full report)

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Flaky tests (3)

Postgres 16

• test_storage_controller_smoke: debug
• test_subscriber_restart: release

Postgres 15

• test_pageserver_restarts_under_worload: release

Code coverage* (full report)

• functions: 31.6% (6626 of 20990 functions)
• lines: 48.6% (51493 of 106045 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
357918b at 2024-06-11T21:41:05.264Z :recycle:}

[VladLazar]

Looking at the code, the scrubber is S3 specific (it creates an s3 client). To my mind it would make more sense to make it generic first and rename it later. I don't mind too much though.

[arpad-m]

Yeah currently it's S3 specific in the implementation but I have done first steps in an open PR: #7932

We already use internally the new name, and I'd like the current/old name to not proliferate (and we are about to proliferate it further judging https://github.com/neondatabase/cloud/issues/14024 ).

[VladLazar]

I see no harm in merging this, but doing it now feels a bit awkward to me. In any case, feel free to merge.