Extract Ci::Minutes::Quota class

What does this MR do?

Related to #213964 (closed)

This MR represents the first stab at extracting CI minutes logic into a dedicated class.

The current state of the code has several problems:

1. Currently this logic is spread across methods in Namespace, NamespaceStatistics and NamespacesHelper classes.
2. These with methods cross reference each other in a way that is hard to understand the logic.
3. All methods are public, so they are all potentially being used in the view, making refactoring difficult.
4. Test coverage for some of these methods is low given the criticality around purchased CI minutes.

In this MR I've created Ci::Minutes::Quota class that implements the logic from NamespacesHelper and other related methods from Namespace and NamespaceStatistics. This is only the first iteration as a lot of the minutes logic is still around the place. Most of the methods are already implemented in Ci::Minutes::Quota but not used yet. This is the goal of future iterations.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team