Add gitlab_runner Resource

[RicePatrick]

Description

This PR adds support for registering runners using a gitlab_runner resource.

Closes #49

PR Checklist Acknowledgement

• I acknowledge that all of the following items are true, where applicable:
  • Resource attributes match 1:1 the names and structure of the API resource in the GitLab API documentation.
  • Examples are updated with:
    • A *.tf file for the resource/s with at least one usage example
    • A *.sh file for the resource/s with an import example (if applicable)
  • New resources have at minimum a basic test with three steps:
    • Create the resource
    • Update the attributes
    • Import the resource
  • No new //lintignore comments were copied from existing code. (Linter rules are meant to be enforced on new code.)

[RicePatrick]

unfortunately, there are a couple new lintignore issues since there are boolean values here which require the use of GetOkExists, which is a deprecated method ☹️

[RicePatrick]

@armsnyder | @timofurrer - This is ready for review/merger.

[timofurrer]

@PatrickRice-KSC looks pretty solid already, thanks!

There are a few copy & paste mistakes, nitpicks / styling stuff and other minor things.

Regarding the GetOkExists() - that's not a problem at all - IMHO it's still the best option we have with the current SDK and there will be a replacement before they delete it, thus all good.

Back to you 🏓

[timofurrer]

Thanks for the good work @PatrickRice-KSC once again!

LGTM 🎉

[github-actions]

This functionality has been released in v3.15.0 of the Terraform GitLab Provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading.

For further feature requests or bug reports with this functionality, please create a new GitHub issue. Thank you!