add personal_access_token resource

Affected Resource(s)

• new: personal_access_token

With the GitLab Users API supporting personal access tokens for a user it would be helpful to be able to manage some of these via terraform. This is especially helpful with service accounts as this token can then be used to configure a service in another application that is not GitLab

Important Factoids

• go-gitlab already has the capability to create personal access tokens.
• Revoking & Listing tokens for a user is a separate API call not apart of the users api. go-gitlab work would need to be done
• Before this can happen as we would want to be able to query the tokens that are created after the initial deployment
• This is applicable to all license tiers

Relevant Links

• https://github.com/xanzy/go-gitlab/blob/master/users.go#L838
• https://docs.gitlab.com/ee/api/personal_access_tokens.html
• https://docs.gitlab.com/ee/api/users.html#create-a-personal-access-token