Display code coverage approval rule in project settings

Problem to solve

We are creating a custom approval rule similar to License Check and Vulnerability Check approval rules (see #15765 (closed)). As part of this, we need to implement the frontend project setting so that the user can enable this approval rule.

Proposal

We will need to coordinate with the backend to create a new approval rule setting. We can follow the pattern set out in the security approval rules which is laid out in:

• https://gitlab.com/gitlab-org/gitlab/-/blob/421d10b7e7f79bd687d08555031ebaf352405e21/ee/app/assets/javascripts/approvals/components/project_settings/project_rules.vue
• https://gitlab.com/gitlab-org/gitlab/-/blob/421d10b7e7f79bd687d08555031ebaf352405e21/ee/app/assets/javascripts/approvals/components/security_configuration/unconfigured_security_rules.vue

Issue for creating the rule: #331001 (closed)

Here is a previous MR implementing this for security: !38992 (merged)