Re-organise maven fixtures

What does this MR do and why?

Describe in detail what your merge request does and why.

To add a test that verifies the Maven request forwarding feature, a few changes on file management files for maven to push and pull packages are needed. This leverages the power of using fixtures like in other package managers, organizing them by endpoint and by the producer (project that deploys a package) and consumer (project that installs a package).

This change will allow adding a test that requires new fixtures in a more readable and maintainable way.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.