set isDefault to be readonly and make its default value - false.
Alter table - default.
Updated release notes.
Merge branch 'IX-9.20.0' of https://github.com/kaltura/server into IX-9.20.0-delivery-profiles

Conflicts:
	release-notes.md
Updated release notes
Merge pull request #1501 from kaltura/IX-9.20.0-delivery-profiles

Ix 9.20.0 delivery profiles