[Documentation] Add documentation updates for project-level exclusions

Overview

This issue tracks the documentation changes for the Phase 1: Add ability to manage exclusions of pa... (&14878 - closed) • Unassigned

Proposal

The feature details can be listed under https://docs.gitlab.com/ee/user/application_security/secret_detection/secret_push_protection.

We should cover the following details:

• Specify the current exclusion implementation should allow user to configure only at project level.
• Specify that only maintainers and owners of projects have the ability to manage exclusions.
  • Also, developers and auditors can read the exclusions but cannot manage them.
• Add details of all types of exclusions accepted with an example:
  • Exclude secrets matching file paths.
  • Exclude secrets matching rules from default ruleset.
  • Exclude secrets matching raw values.