add authentication rate limiting

[conradludgate]

Problem

https://github.com/neondatabase/cloud/issues/9642

Summary of changes

1. Make EndpointRateLimiter generic, renamed as BucketRateLimiter
2. Add support for claiming multiple tokens at once
3. Add AuthRateLimiter alias.
4. Check (Endpoint, IP) pair during authentication, weighted by how many hashes proxy would be doing.

TODO: handle ipv6 subnets. will do this in a separate PR.

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]

2718 tests run: 2580 passed, 0 failed, 138 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_vm_bit_clear_on_heap_lock: debug

Code coverage* (full report)

• functions: 28.1% (6295 of 22372 functions)
• lines: 47.0% (44269 of 94190 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
7e584d6 at 2024-03-25T18:25:11.222Z :recycle:}