compute <-> sk protocol v3

[arssher]

Problem

As part of #8614 we need to pass membership configurations between compute and safekeepers.

Summary of changes

Add version 3 of the protocol carrying membership configurations. Greeting message in both sides gets full conf, and other messages generation number only. Use protocol bump to include other accumulated changes:

• stop packing whole structs on the wire as is;
• make the tag u8 instead of u64;
• send all ints in network order;
• drop proposer_uuid, we can pass it in START_WAL_PUSH and it wasn't much useful anyway.
  Per message changes, apart from mconf:
• ProposerGreeting: tenant / timeline id is sent now as hex cstring. Remove proto version, it is passed outside in START_WAL_PUSH. Remove postgres timeline, it is unused. Reorder fields a bit.
• AcceptorGreeting: reorder fields
• VoteResponse: timeline_start_lsn is removed. It can be taken from first member of term history, and later we won't need it at all when all timelines will be explicitly created. Vote itself is u8 instead of u64.
• ProposerElected: timeline_start_lsn is removed for the same reasons.
• AppendRequest: epoch_start_lsn removed, it is known from term history in ProposerElected.

Both compute and sk are able to talk v2 and v3 to make rollbacks (in case we need them) easier; neon.safekeeper_proto_version GUC sets the client version. v2 code can be dropped later.

So far empty conf is passed everywhere, future PRs will handle them.

To test, add param to some tests choosing proto version; we want to test both 2 and 3 until we fully migrate.

ref #10326

[github-actions]

7447 tests run: 7093 passed, 0 failed, 354 skipped (full report)

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Flaky tests (1)

Postgres 16

• test_pageserver_catchup_while_compute_down: release-arm64-with-lfc

Code coverage* (full report)

• functions: 33.2% (8580 of 25863 functions)
• lines: 49.1% (72376 of 147537 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
748bb5d at 2025-02-07T11:55:16.429Z :recycle:}

[knizhnik]

I missing something but doesn't proto_version == SK_PROTO_VERSION_3 handled in the condition above?
Also I believe comment should be // TODO remove proto_version == 2

[arssher]

Thanks, indeed forgot to remove it. I was just using proto_version == SK_PROTO_VERSION_3 to test things before all messages were made into v3. Fixed.