Finalize virtual_registries_packages_maven_cache_entries table changes

🔥 Problem

In Set up partitioning for maven virtual registry ... (!174985 - merged) , we introduce a new table (virtual_registries_packages_maven_cache_entries) as a way to introduce partitioning for cache entries.

By doing so, we intentionally left to a side, additional cleanup tasks. The main reason is that the MR was already large enough. In addition, this additional cleanup tasks need to happen in a different milestone than the one introducing the table. This is to make sure to maintain a retro compatibility.

🚒 Solution

Implement the clean tasks:

• Drop the old table virtual_registries_packages_maven_cached_responses.
  • Remove the related LFKs.
• Remove the Group LFK for groups -> virtual_registries_packages_maven_cache_entries.
• Rename the models, services class. Eg VirtualRegistries::Packages::Maven::CachedResponse.
  • Rename the related helper classes (specs and other files).

⚠️ Do it, one milestone after the one where !174985 (merged) was delivered.