CBG-4849: updates to api docs for ISGR

[gregns1]

CBG-4849

• Details the new default policy
• Note to remove the _rev and _cv properties for doc merges.

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Dependencies (if applicable)

• Link upstream PRs
• Update Go module dependencies when merged

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGatewayIntegration/0000/

[github-actions]

Redocly previews

• Admin API
• Public API
• Metric API
• Diagnostic API

[Copilot]

Pull Request Overview

This PR updates the API documentation for Inter-Sync Gateway Replication (ISGR) to reflect changes in Sync Gateway 4.x, specifically updating the default conflict resolution policy and adding guidance for document merges.

Key changes:

• Updates default conflict resolution policy documentation to distinguish between pre-4.x and 4.x+ behavior
• Adds note about excluding _rev and _cv properties when performing document merges in custom conflict resolvers

[torcolvin]

Do we ever explain in the public documentation what _rev and _cv are in the custom conflict resolver section? I can see that we don't because it's hard to know how you would use them, but are they visible to users who might want to do something like custom merge if there is a flag, or LWW otherwise?

What happens if you include _rev or _cv? Does ISGR reject this document?