refactor(scrubber): add unified command suitable for cron job

[yliang412]

Part of #8128.

Description

This PR creates a unified command to run both physical gc and metadata health check as a cron job. This also enables us to add additional tasks to the cron job in the future.

❯ cargo run --bin storage_scrubber -- cron-job --help
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.32s
     Running `target/debug/storage_scrubber cron-job --help`
Usage: storage_scrubber cron-job [OPTIONS] --min-age <GC_MIN_AGE>

Options:
      --min-age <GC_MIN_AGE>  
  -g, --gc-mode <GC_MODE>     [default: indices-only] [possible values: dry-run, indices-only, full]
      --post                  
  -h, --help                  Print help

Checklist before requesting a review

• I have performed a self-review of my code.
• If it is a core feature, I have added thorough tests.
• Do we need to implement analytics? if so did you add the relevant metrics to the dashboard?
• If this PR requires public announcement, mark it with /release-notes label and add several sentences in this section.

Checklist before merging

• Do not forget to reformat commit message to not include the above checklist

[github-actions]

2172 tests run: 2103 passed, 0 failed, 69 skipped (full report)

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Flaky tests (1)

Postgres 16

• test_scrubber_physical_gc_ancestors_split: debug

Code coverage* (full report)

• functions: 32.4% (7231 of 22306 functions)
• lines: 50.4% (58488 of 116119 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
cae5641 at 2024-08-17T15:56:33.181Z :recycle:}