Add query execution time histogram

[knizhnik]

Problem

It will be useful to understand what kind of queries our clients are executed.
And one of the most important characteristic of query is query execution time - at least it allows to distinguish OLAP and OLTP queries. Also monitoring query execution time can help to detect problem with performance (assuming that workload is more or less stable).

Summary of changes

Add query execution time histogram.

[github-actions]

8525 tests run: 7942 passed, 0 failed, 583 skipped (full report)

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Flaky tests (6)

Postgres 16

• test_pageserver_reconnect: release-arm64-with-lfc
• test_sharding_split_failures[failure2]: release-arm64-with-lfc

Postgres 15

• test_backward_compatibility: release-arm64-with-lfc

Postgres 14

• test_sharding_split_failures[failure10]: release-arm64-with-lfc
• test_sharding_split_failures[failure7]: release-arm64-with-lfc
• test_sharding_split_failures[failure12]: release-arm64-with-lfc

Code coverage* (full report)

• functions: 32.3% (9063 of 28081 functions)
• lines: 48.6% (80104 of 164866 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
333764f at 2025-06-05T08:55:01.860Z :recycle:}

[github-actions]

If this PR added a GUC in the Postgres fork or neon extension,
please regenerate the Postgres settings in the cloud repo:

make NEON_WORKDIR=path/to/neon/checkout \
  -C goapp/internal/shareddomain/postgres generate

If you're an external contributor, a Neon employee will assist in
making sure this step is done.