Fork pgtap-docker to support arm64 (#2411)

* feat(sql): Fork pgtap to support arm64

This forks pgtap-docker and builds the image locally,
and updates our references to use our forked image.

* fixup! feat(sql): Fork pgtap to support arm64

testing/dbtest/pgtap-docker/README.md

@@ -0,0 +1,7 @@
+# pgtap-docker
+
+The code in this folder is a hard fork of https://github.com/subzerocloud/pgtap-docker.
+The LICENSE included at the root of this folder apply to the contents of this folder ONLY.
+
+The code is changed to support building the docker image for multiple Docker platforms (e.g. linux/arm64)
+and to update versions and remove deprecated fields.