.pullapprove.yml: Switch to v2 and other project-template updates
.pullapprove.yml: Switch to v2 and other project-template updates

Pull in changes from [1].  The only changes vs. the upstream version
are:

* Kept the image-spec-specific approve_regexp.
* Removed all the groups except for the image-spec group.

[1]: https://github.com/opencontainers/project-template/pull/29

Signed-off-by: W. Trevor King <f75897670c17327c42ab201733fb8a81ff9f4c34@tremily.us>

vbatts/oci-image-spec,mattspencer-arm/image-spec,jonboulle/image-spec,vbatts/oci-image-spec,opencontainers/image-spec,jonboulle/image-spec,mattspencer-arm/image-spec,opencontainers/image-spec