Make Postgres 16 default version

[bayandin]

Problem

The default Postgres version is set to 15 in code, while we use 16 in most of the other places (and Postgres 17 is coming)

Summary of changes

• Run benchmarks job with Postgres 16 (instead of Postgres 14)
• Set DEFAULT_PG_VERSION to 16 in all places
• Remove deprecated --pg-version pytest argument
• Update test_metadata_bincode_serde_ensure_roundtrip for Postgres 16

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]

2252 tests run: 2178 passed, 0 failed, 74 skipped (full report)

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Flaky tests (1)

Postgres 16

• test_layer_bloating: debug

Code coverage* (full report)

• functions: 32.4% (7222 of 22268 functions)
• lines: 50.4% (58312 of 115744 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
211c7b2 at 2024-08-16T12:40:04.582Z :recycle:}