storcon: squash all migrations into one

[VladLazar]

Problem

Neon and Hadron deployments have the same database schema, but different migration histories. Some transactions have different identifiers too. If we don't do anything about it, then the storage controller would fail to apply the merged set of transactions.

Summary of Changes

We squash all migrations into a single one. If the schema already matches, then the new transaction gets applie without doing anything. For new regions, this migration will bootstrap the database schema.

This should be merged in both neon and hadron codebases.

Note that after deploying this change, the __diesel_schema_migrations table will still contain entries for the old pre-squash transactions. This is fine because diesel only considers the tranasactions embedded in the repo for application. Once we are certain that we are not going to roll back, we can clean up the __diesel_schema_migrations tables in prod, but this is manual and error prone, so I'd skip it.

Rolling back

Rolling back to a previous deployment which embeds the non-squashed transactions is safe. The old transactions are still present in __diesel_schema_migrations (i.e. considered applied), so no migrations will be run, so no migrations will be run.

Note that this assumes that all transactions are applied and squashed into the new migration before deployment.

Touches LKB-2482

[github-actions]

9119 tests run: 8466 passed, 0 failed, 653 skipped (full report)

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Flaky tests (2)

Postgres 17

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

Postgres 16

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

Code coverage* (full report)

• functions: 34.7% (8838 of 25472 functions)
• lines: 45.7% (71635 of 156659 lines)

* collected from Rust tests only

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_{The comment gets automatically updated with the latest test results
89231e3 at 2025-07-31T13:55:51.903Z :recycle:}