ReviewApps: CI pin external-dns to 2.x version

What does this MR do?

Pin the version of deployed external-dns to 2.y.z, using SemVer matching. (^2.2.1)

Update the properties for the service account keys per Upgrading to 2.0.0 of the stable/external-dns README.

Add aws.batchChangeSize=400 to combat messages about RDATA being too large.

Closes #64356 (closed)

/label groupdistribution

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Separation of EE specific content

Closes #64356 (closed)

cc @twk3