proxy: add http2 support

[conradludgate]

Problem

Proxy already supported HTTP2, but I expect no one is using it because we don't advertise it in the TLS handshake.

WebSockets over HTTP2 is a different story and we need more explicit handling of it. Thankfully the protocol is exactly the same, just the handshake is different.

Summary of changes

1. Add protocol list for h2 and http/1.1
2. vendor hyper-tungstenite implementation
3. introduce extended connect handshake for websockets over http2

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]

2256 tests run: 2171 passed, 0 failed, 85 skipped (full report)

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Flaky tests (3)

Postgres 15

• test_crafted_wal_end[last_wal_record_crossing_segment]: debug
• test_crafted_wal_end[simple]: debug

Postgres 14

• test_delete_tenant_exercise_crash_safety_failpoints[mock_s3-tenant-delete-before-create-remote-mark-True-Check.RETRY_WITH_RESTART]: debug

Code coverage (full report)

• functions: 55.1% (10306 of 18720 functions)
• lines: 81.5% (58717 of 72037 lines)

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_{The comment gets automatically updated with the latest test results
2430612 at 2024-01-12T18:50:56.164Z :recycle:}

[vadim2404]

can we have tests that websocket works on http1.1 and http2?

[conradludgate]

Adding a WS over HTTP2 test will be tricky. Waiting on encode/httpx#304 + encode/httpcore#592.

I'll write an initial rust-based test, but that won't validate it's correct - only that it works writing the rust based test will be tricky