Support feature branch matching for webhook triggered builds

[canny]

If a consumer and provider use matching feature branches to add new features, the webhook could be configured to trigger the matching branch of the provider build, if there was a matching branch known about in the broker. This would mean there wouldn't have to be an intermediate build in the CI to trigger the build with the right branch.

"request": {
    "body": {
      "branch": "${pactbroker.matchingFeatureBranchOrMainDevelopmentBranch}",
      "commit": "HEAD",
      "message": "Build all the things! :rocket:",
      "env": {
        "PACT_URL": "${pactbroker.pactUrl}"
      }
    },
    "method": "POST",
    "url": "https://api.buildkite.com/v2/organizations/<ORG>/pipelines/<PIPELINE>/builds"
  }

https://pact.canny.io/admin/board/feature-requests/p/support-feature-branch-matching-for-webhook-triggered-builds

[canny]

This issue has been linked to a Canny post: Support feature branch matching for webhook triggered builds 🎉