First version of a new benchmark to test larger OLTP workload

[Bodobolero]

Problem

We want to support larger tenants (regarding logical database size, number of transactions per second etc.) and should increase our test coverage of OLTP transactions at larger scale.

Summary of changes

Start a new benchmark that over time will add more OLTP tests at larger scale.
This PR covers the first version and will be extended in further PRs.

Also fix some infrastructure:

• default for new connections and large tenants is to use connection pooler pgbouncer, however our fixture always added statement_timeout=120 which is not compatible with pooler see
• action to create branch timed out after 10 seconds and 10 retries but for large tenants it can take longer so use increasing back-off for retries

Test run

/~https://github.com/neondatabase/neon/actions/runs/13593446706

[github-actions]

7744 tests run: 7365 passed, 0 failed, 379 skipped (full report)

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Flaky tests (1)

Postgres 15

• test_compute_pageserver_connection_stress: release-x86-64-with-lfc

Code coverage* (full report)

• functions: 32.8% (8646 of 26375 functions)
• lines: 48.6% (73222 of 150679 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
de6bfde at 2025-02-28T20:44:11.217Z :recycle:}