SNAPSHOT: Use CancellableThreads to Abort

[original-brownbear]

• Closes Use CancellableThreads to abort snapshots #21759

[elasticmachine]

Pinging @elastic/es-distributed

[ywelsch]

This depends on #32512

[original-brownbear]

@ywelsch maybe I can just move this to using ActionListener instead of CompletableFuture, I wasn't aware of #32512 when I opened this, but it seems I can do the same thing with ActionListener just fine :)?

[ywelsch]

I'm inclined not to go forward with this, as we're unaware of the consequences of interrupting threads in the third-party SDKs that we're using.

[original-brownbear]

Right, closing here :) Will investigate making this async instead.