Feature Request: support add prefix to checkpoint table names.

[sillydong]

Hi, as you can see, in both PostgreSQL checkpoint implementation, the table names are fixed. It is forced to use checkpoint_migrations, checkpoint_blobs, checkpoint_writes to store all data. What if these names are already exist in the database? There will be conflicts when setting up this. So I'm suggesting we can add a common prefix before the table names. By adding the prefix, we can support using existing database with checkpoint* name and we can also support save multiple agents' checkpointer into one database.
This idea is also posted in langgraph-checkpoint-mysql repo, see tjni/langgraph-checkpoint-mysql#67