Add triage and maintain repo permissions

[liamg]

Closes #279

This PR makes the triage and maintain repository permissions available. See https://github.blog/2019-10-03-delegate-responsibilities-with-expanded-repository-permissions/

[kpfleming]

Note that this PR contains the same (unrelated) fix as in #310. We really need that one merged so everyone can stop making this same change in their branches :-)

[alexbde]

Looks like #296 is another duplicate of this. Please merge one of them :)

[alexbde]

Closes #270.

[majormoses]

LGTM

[salvianreynaldi]

Hi,
the code seems to address both github_team_repository and github_repository_collaborator. However, I get errors when trying to set repository collaborator:

unexpected permission value: triage
unexpected permission value: maintain

Terraform set the permissions correctly, though. However, I can't then modify the permission (e.g. from maintain/triage to pull) in terraform, it gives the same error message, and the permissions are not updated this time.

This doesn't happen with the team repository. Am I missing something?

[paultyng]

@salvianreynaldi not that I'm aware of, this is working for me now, but I do occasionally get unexpected diffs with different permission strings, but it doesn't seem to affect the actual runtime permissions available to people. I haven't dug in to the diff/read issue yet to figure out the reason for that, it may be related.

If you can though, I'd recommend opening a new issue with a repro if you have one, or at least a log.

[romaninsh]

I believe something needs to be changed either here:

https://github.com/terraform-providers/terraform-provider-github/blob/895ed90a8b43c1befc7c9c598d5a54fa4107cb30/github/resource_github_repository_collaborator.go#L117

or here: https://github.com/terraform-providers/terraform-provider-github/blob/8c9a8c3892278e7a32fda6b8744190994722db33/github/util_permissions.go#L45-L51

Will try to play around. API reference: https://github.com/terraform-providers/terraform-provider-github/blob/8c9a8c3892278e7a32fda6b8744190994722db33/github/util_permissions.go#L51

Also this needs adjusting: https://github.com/romaninsh/terraform-provider-github/blob/master/website/docs/r/repository_collaborator.html.markdown#argument-reference

[anGie44]

Fix to be released in the upcoming v2.8.0 release.