Add group code coverage download button

What does this MR do?

This MR adds a new page for Group Repositories Analytics, adds a link to the page in the sidebar for a group, adds a Test Code Coverage section, and adds a button to click to download a CSV of the coverage history for the projects in the group. Group Repository Analytics is a GitLab Premium feature and we will add more content to this page in the near future.

⚠ This MR depends on !38520 (merged) to provide the CSV data, without it the CSV is blank

Documentation: this MR adds a Repositories analytics **(PREMIUM) section to the docs page for groups and a Repositories Analytics **(PREMIUM)** page with more details about the CSV that is available to download. We can expand this page with more documentation as we build more features.

For more context, see #215104 (closed)

Things left to do

• Plug in the download path once we know what it is
• Replace if true line in groups_helper.rb with the proper permission/feature check
• Write documentation

Screenshots

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