Updates to replay docs for mass-replay features

[Sushisource]

What does this PR do?

Update docs on replay to include some advice about CI, and how to use new multiple-history replay APIs.

Notes to reviewers

DRAFT until we have the new list workflow APIs, since that affects the whole flow. If we end up releasing SDKs without that, but with the new mass-replay stuff, we can update this to leave it out for now.