Currently the merge script default branch configuration throws an error
if an unexpected version branch is discovered. The error right now
assumes to much knowledge of the logic and the document outlining
the release trains conceptually.
We change it to something more easy to understand that doesn't require
full understanding of the versioning/labeling/branching document that
has been created for the Angular organization.
PR Close#38622
Previously, each Angular repository had its own strategy/configuration
for merging pull requests and cherry-picking. We worked out a new
strategy for labeling/branching/versioning that should be the canonical
strategy for all actively maintained projects in the Angular organization.
This PR provides a `ng-dev` merge configuration that implements the
labeling/branching/merging as per the approved proposal.
See the following document for the proposal this commit is based on
for the merge script labeling/branching: https://docs.google.com/document/d/197kVillDwx-RZtSVOBtPb4BBIAw0E9RT3q3v6DZkykU
The merge tool label configuration can be conveniently accesed
within each `.ng-dev` configuration, and can also be extended
if there are special labels on individual projects. This is one
of the reasons why the labels are not directly built into the
merge script. The script should remain unopinionated and flexible.
The configuration is conceptually powerful enough to achieve the
procedures as outlined in the versioning/branching/labeling proposal.
PR Close#38223
Paul Gschwendtner