Operator can fetch/generate component release manifests from commits/pull-requests/branches

At present, tektoncd/operator fetch payload mechanism can take only github tags (release versions) as inputs. This restricts our ability to run operator e2e tests with latest changes any of our components (eg: pipelines).

If we can provide a way to specify other inputs like PRs, commits, branch names to fetch-payload mechanism, then we can run tests on downstream OpenShift clusters easily. This means we can test out a change from a tektoncd/pipelines PR using operator on OpenShift.

Acceptance Criteria

• fetch-payload script can take commits, PullRequests, branchnames ... as inputs for fetching/generating component installation manifests.