* Add a branch regex to the repo.yaml config to allow Atlantis to
accept only pull requests with a given base branch (the branch
a PR would merge _into_).
* `branch` is optional. By default its unset and Atlantis will match
webhooks for pull requests for any branch (no change)
Match any PR,
```
repos:
- id: /.*/
branch: /.*/
```
Match only PRs with master or main base branch.
```
repos:
- id: /.*/
branch: /(main|master)/
```
Some repos have special pull request branching practices. For example,
plan/apply from feature branches merging into master, but separate flows
for merging master into a release branch (where Atlantis isn't used).
Adding a regex allows for flexible workflow options. For example, you
could have Atlantis ignore "release" branches.
