[sdk-wide] go get -u all + go mod tidy automation

[richardpark-msft]

Our goal here is just to have it happen on a weekly cadence, with the merge happening automatically and the testing in the weekly pipeline to validate.

Weekly pipelines for a package should do this:

1. go get -u all
2. go mod tidy
3. Run tests
4. git commit go.mod go.sum
5. git push

Steps 4 and 5 are probably new, but we believe some teams must have some process like this in place (for instance, Java) so hopefully we can lean a bit on what they've done.

CC: @benbp, @alzimmermsft (who probably has heard of something like this for Java)

[benbp]

@richardpark-msft @jhendrixMSFT we have a pretty similar example of this already working in the go repo for the post-release steps: https://github.com/Azure/azure-sdk-for-go/blob/main/eng/pipelines/templates/jobs/archetype-go-release.yml#L112-L120

[benbp]

If you want to push to main directly we have this template: https://github.com/Azure/azure-sdk-tools/blob/main/eng/common/pipelines/templates/steps/git-push-changes.yml

The weekly pipelines already appear to be wired up with github permissions.