Add gitlab_user_impersonation_token

New Resource

I am missing support for impersonation tokens. I have bot accounts and I want to generate tokens for them as an admin. Impersonation token is the straight-forward way to do it.

There was an attempt to implement it in !332 (closed), but it never got finished.

Related GitLab APIs

• API documentation: https://docs.gitlab.com/ee/api/users.html#create-an-impersonation-token
• go-gitlab implementation: https://github.com/xanzy/go-gitlab/blob/f0095cdf967ab4a8bb4cd4428dfeb49e72f0599d/users.go#L1283
• go-gitlab example: https://github.com/xanzy/go-gitlab/blob/f0095cdf967ab4a8bb4cd4428dfeb49e72f0599d/examples/impersonation.go

Additional Details

• GitLab REST API resources available (read for data sources, crud for resources)
• go-gitlab does support the related GitLab API already
• I'd like to contribute it myself