storcon: switch to diesel-async and tokio-postgres

[arpad-m]

Switches the storcon away from using diesel's synchronous APIs in favour of diesel-async.

Advantages:

• less C dependencies, especially no openssl, which might be behind the bug: https://github.com/neondatabase/cloud/issues/21010
• Better to only have async than mix of async plus spawn_blocking

We had to turn off usage of the connection pool for migrations, as diesel migrations don't support async APIs. Thus we still use spawn_blocking in that one place. But this is explicitly done in one of the diesel-async examples.

[github-actions]

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a661209 at 2025-01-15T01:18:19.983Z :recycle:}

[arpad-m]

Reconcile error: Cannot perform this operation while a transaction is open

not sure what the cause could be, I did a 1:1 translation, except that we don't start a transaction for running the migrations because of weiznich/diesel_async#115 . but that happens on an entirely separate connection from the reconciler where the issue occurs.

[conradludgate]

I was curious so I tried with 1.85 with AsyncFn. It almost works, but there seems to be a limitation in proving Send bounds. I also had to manually implement the logic of TransactionManager.

[arpad-m]

I had Send issues as well, what worked is adding a Sync requirement. Not really beautiful, but it works :).

[arpad-m]

Made it use r2d2 instead, but no avail, now it times out in the run function of TransactionBuilder when trying to figure out who the current leader is (basically hangs there).