No-op to idempotency table when table is empty on boot

[slinkydeveloper]

Completely disable codepaths using IdempotencyTable when the key space of idempotency table is empty. We can do so because in the next release, no one will write to the idempotency table key space anymore, so if the table is empty will remain empty for the rest of the execution.

We can probably add a check for that when initializing the PartitionStore.

Essentially like https://github.com/restatedev/restate/issues/2186 for idempotency table

[zhaohaidao]

If no one is solving it, I'd like to try