compute_ctl: database_schema should keep process::Child as part of returned value

[prepor]

Problem

/database_schema endpoint returns incomplete output from pg_dump

Summary of changes

The Tokio process was not used properly. The returned stream does not include process::Child, and the process is scheduled to be killed immediately after the get_database_schema call when cmd goes out of scope.

A simple solution is to remove .kill_on_drop(true) and add cmd.await to the spawned task. While this approach should work fine, it forfeits the useful property of automatically killing unnecessary processes when HTTP connections are closed.

An alternative solution I propose is to return a special Stream implementation that retains process::Child.

What do you think? If the simpler solution is preferred, I can update this PR accordingly.

[github-actions]

7260 tests run: 6895 passed, 0 failed, 365 skipped (full report)

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Flaky tests (2)

Postgres 16

• test_physical_replication_config_mismatch_max_locks_per_transaction: release-arm64

Postgres 15

• test_parallel_copy: release-arm64

Code coverage* (full report)

• functions: 31.1% (8412 of 27008 functions)
• lines: 47.8% (66788 of 139612 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
47a3cbd at 2025-01-09T13:44:16.257Z :recycle:}