Recreate gitlab_project_variable if it was manually deleted

Created by: MajorBreakfast

Hello,

I just ran into the issue that planning fails with the following error if a previously created project variable has been manually deleted. It would be better if the provider recreated the variable instead of failing.

Error: GET https://gitlab.example.com/api/v4/projects/81/variables/MY_VARIABLE: 404 {message: 404 Variable Not Found}

• Terraform version: 0.12.23
• GitLab provider version: 2.5.0
• Affected Resource(s)
  • gitlab_project_variable
  • gitlab_group_variable (likely) (Edit: Confirmed. See first comment)