Run a go linter as a GitHub action

[reedy]

For example:

https://github.com/golangci/golangci-lint

https://golangci-lint.run/usage/install/#ci-installation

Filed as part of https://phabricator.wikimedia.org/T292110

[reedy]

Can potentially do #4 as part of this issue

[miselico]

I have now added golangci-lint to the workflow. It did indicate some issues already, most of them seem trivial to fix.
I have not investigated how to run tests with this yet.

[miselico]

Since 06c4a15 the linter is run as part of the github workflow upon creation of a pull request, merging into main and scheduled once every week on main.