`pdk update` should warn if pinned to old version of template

If a user has as some point used the `--template-ref` option to manually pin their template ref to a version tag, `pdk update` will no longer track template versions using `pdk --version`, so the user will no longer be updating their module.

We should consider at least issuing a WARN if the tracked `template-ref` in metadata.json looks like a version tag, but does not == the value of `pdk --version` so that the user will know why their module is not updating. The warning should also include directions for how to resolve the situation.