proxy: Create disconnect events

[khanova]

Problem

It's not possible to get the duration of the session from proxy events.

Summary of changes

• Added a separate events folder in s3, to record disconnect events.
• Disconnect events are exactly the same as normal events, but also have disconnect_timestamp field not empty.
• @oruen suggested to fill it with the same information as the original events to avoid potentially heavy joins.

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]

2820 tests run: 2699 passed, 0 failed, 121 skipped (full report)

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Flaky tests (1)

Postgres 16

• test_vm_bit_clear_on_heap_lock: debug

Code coverage* (full report)

• functions: 28.2% (6554 of 23272 functions)
• lines: 46.8% (46289 of 98859 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
916a3e6 at 2024-04-29T12:53:44.887Z :recycle:}