pageserver: make control_plane_api & generations fully mandatory

[jcsp]

Problem

We had retained the ability to run in a generation-less mode to support test_generations_upgrade, which was replaced with a cleaner backward compat test in #10701

Summary of changes

• Remove all the special cases for "if no generation" or "if no control plane api"
• Make control_plane_api config mandatory

[github-actions]

7425 tests run: 7067 passed, 0 failed, 358 skipped (full report)

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Flaky tests (2)

Postgres 17

• test_s3_wal_replay: release-arm64-with-lfc

Postgres 14

• test_scrubber_physical_gc_ancestors[None]: release-arm64-with-lfc

Code coverage* (full report)

• functions: 33.3% (8585 of 25819 functions)
• lines: 49.1% (72287 of 147221 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
814f47b at 2025-02-07T14:50:36.257Z :recycle:}

[jcsp]

docker-compose.yml was still relying on creating a pageserver with no config