Move Pipelines quota to Pipelines (CI/CD) in Settings page for groups
### Description
For groups, we have pipelines quota as a standalone page under settings.
Since we now have **Settings > Pipelines** (will be **Settings > CI/CD**) for group-level variables, we can consider to move pipelines quota in the same submenu.
### Proposal
Move **Settings > Pipelines quota** in **Settings > Pipelines**
### Feature checklist
Make sure these are completed before closing the issue,
with a link to the relevant commit.
- [ ] [Feature assurance](https://about.gitlab.com/handbook/product/#feature-assurance)
- [ ] Documentation
- [ ] Added to [features.yml](https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/data/features.yml)
issue