Add, remove, rename labels to repos

[snomos]

gut already has support for setting and updating topics. But it is lacking support for doing similar things with labels. To get consistent bug reporting and classification behavior across all repos, it would be best to have a consistent set of labels, and to get that it would be easiest to do that using gut.

There is support for these features in the Github API: https://docs.github.com/en/free-pro-team@latest/rest/reference/issues#list-labels-for-a-repository and below