[CT-2398] Automate changelog consolidating when cutting the first rc

[emmyoop]

When we cut the first rc we want to collapse all beta release changelogs into the single rc changelog. We already do this when we cut the final release. This is the pattern we want.

1.5.0b3
- changelog 5
- changelog 6

1.5.0b2
- changelog 3
- changelog 4

1.5.0b1
- changelog 1
- changelog 2

to the rc

1.5.0rc2
- changelog 10
- changelog 11

1.5.0rc1
- changelog 1
- changelog 2
- changelog 3
- changelog 4
- changelog 5
- changelog 6
- changelog 7
- changelog 8
- changelog 9

to the final

1.5.0

- changelog 1
- changelog 2
- changelog 3
- changelog 4
- changelog 5
- changelog 6
- changelog 7
- changelog 8
- changelog 9
- changelog 10
- changelog 11
- changelog 12

Determine if it's best to do this when we cur the branch (cut-release-branch.yml) or during the actual release. I learn toward during the actual release to ensure we capture all the changelogs in case we need to backport anything.