Clean up 'attachment service' names to storage controller

[jcsp]

The binary etc were renamed some time ago, but the path in the source tree remained "attachment_service" to avoid disruption to ongoing PRs. There aren't any big PRs out right now, so it's a good time to cut over.

• Rename attachment_service to storage_controller
• Move it to the top level for symmetry with storage_broker & to avoid mixing the non-prod neon_local stuff (control_plane/) with the storage controller which is a production component.

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]

2754 tests run: 2630 passed, 0 failed, 124 skipped (full report)

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Code coverage* (full report)

• functions: 28.0% (6396 of 22872 functions)
• lines: 46.8% (45022 of 96134 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
684a835 at 2024-04-05T13:55:53.713Z :recycle:}