changefeedccl: rename/deprecate min_checkpoint_frequency option

We should consider renaming the `min_checkpoint_frequency` option since its name could be misleading. It doesn't control how frequently the changefeed checkpoints but rather how frequently a change aggregator flushes its progress to the change frontier.

https://github.com/cockroachdb/cockroach/blob/c47ab2ca71a5264f7a40e2a6bd2fd7c9cd0a7648/pkg/ccl/changefeedccl/changefeed_processors.go#L870-L882

Alternatively, maybe we should deprecate this option since this is very much a low-level implementation detail and could be derived from more high-level settings like `resolved`.

Jira issue: CRDB-46299