Ability to customize audit user permissions / Create custom user level

Description

Ability to customize the permissions of auditor use. Or the ability to create custom user levels.

Proposal

Allow for GitLab admins to either customize the auditor user permissions or create custom user levels.

Would like the ability to specify whether they could have read-only access to repos and be able to select which API calls the user level is allowed to make.

Use Cases:

1. We would like the audit user more customizable. IE, to select if the user should have repo read access or not, as well as the ability to least all API calls and select what calls the user can and cannot make.
2. The second case to more granular permissions in general. GitLab has the out of the box roles, guest, reporter, developer, etc, but we would request to be able to customize those and create custom roles. For example, we would want to have a role where users (developers, master, and owners) cannot delete branches, but would like a role that includes this.
3. The key ask is to consider the case where you have roles requiring access to SCM/digital assets and those that don't need access but may be involved with administrating other portions of the GitLab pipeline or requiring access to GitLAb metrics. We obviously are required to keep those that have access to all digital assets to an absolute minimum.

Links / references

Customer Ticket -> https://gitlab.zendesk.com/agent/tickets/89203