Consistent group_type

[guyguy333]

Is your feature request related to a problem? Please describe.

Currently, group_type field can be either an integer (harbor_group resource) or a string value (harbor_project_member_group). We cannot easily reuse value from one resource to another.

Describe the solution you'd like

Use a consistent field type for group_type

Describe alternatives you've considered

None

Additional context

[naitmare01]

What makes more sense, using integers as stated in the API or using the custom strings implemented in this provider?

I think it makes more sense to stick to the API and drop the custom strings. This makes it more clear and less error prone and more future proof.

Git blame on the affected rows:
https://github.com/goharbor/terraform-provider-harbor/blame/7453ba31f2174e0e4c3b4e73b3ae23b18204f3d5/client/project_members.go#L33

[dmakeienko]

Same for project_id in resource harbor_project_member_user