Add wlynch to entrypoint OWNERS

wlynch is a Pipelines reviewer with significant famililarity/contributions to the entrypoint.

Our [contributor ladder](https://github.com/tektoncd/community/blob/main/process.md#reviewer)
states that reviewers "Can be allowed to /approve pull requests in specific sub-directories of a project
(by maintainer discretion)". However, this isn't frequently done in Pipelines in practice.
This change will allow us to experiment with more directory-based permissions as a potential pathway
for growing reviewers and approvers for Pipelines.

pkg/entrypoint/OWNERS

@@ -0,0 +1,4 @@
+approvers:
+- wlynch
+labels:
+- area/entrypoint