Improve migration guide

[mojito317]

Checklist

• [x] Tick to sign-off your agreement to the Developer Certificate of Origin (DCO) 1.1
• [ ] Added tests for code changes or test/build only changes
• [ ] Updated the change log file (CHANGES.md|CHANGELOG.md) or test/build only changes
• [x] Completed the PR template below:

Description

My goal was to improve the migration guide dispersing the fog around the support of the retry feature an error handling.

Approach

• applied code style on the links for new operations 7517927ee0261c152aa13f812fc7ae040cae95a3
• fixed incorrect links (8548ee067aeffce6f2b9ff186a3b3432295db9f6):
  • the link for postChanges has changed
  • the link for postPartitionFind has changed
  • postMissingRevs is excluded from the SDKs, I replaced it with postRevsDiff
• Added a warning about the error handling 4103af85a771cbf6a5235b0a7262809873029f5a
• Added a note about Replay adapters replacement 4103af85a771cbf6a5235b0a7262809873029f5a

Schema & API Changes

• "No change"

Security and Privacy

• "No change"

Testing

• N/A build or packaging only changes

Monitoring and Logging

• "No change"