update read committed docs around handling retries

Michael Erickson (michae2) commented:

In 23.2, under read committed isolation, applications could still encounter spurious 40001 errors in rare cases, such as lease transfers. In 24.1, under read committed isolation, we expect applications to encounter ***no*** spurious 40001 errors. (The only 40001 errors applications might encounter are all avoidable through workload changes, such as avoiding deadlocks or increasing `results_buffer_size`.)

This lack of 40001 errors is a special property of read committed isolation, and is definitely worth documenting.

I'm not sure exactly which pages should be updated, but from a quick glance maybe the following:
- https://www.cockroachlabs.com/docs/v24.1/transactions
- https://www.cockroachlabs.com/docs/v24.1/transaction-retry-error-reference
- https://www.cockroachlabs.com/docs/v24.1/read-committed

Jira Issue: DOC-9869