Add filter for branch name on main pipeline page

[uriahcarpenter]

For Pipelines that build a large number of branches, it can get quite cumbersome to find what you're looking for on the pipeline branch page (the buildkite.com/org/pipeline-slug page) if the branch was not recently built.

Adding a filter/search widget (just like the Pipeline dashboard page) that would limit the branches to be a substring of the entered term would improve the user experience a lot.

[petemounce]

Yes, 💯, especially inside a monorepo where there are many people working on many different areas concurrently.