Show package information dependent on tag/branch (like Packagist does)

**Is your feature request related to a problem? Please describe.**
We use the Satis "Required by"-info to check if old packages are unused and can be safely deleted/abandoned.
Since Satis uses **all** repo tags and branches in order to determine the "Required by"-information, the "Required by" list just grows longer and longer (because we don't delete old releases/tags that still contain packages that have been removed in newer tags/releases).

So even if a package is already unused in the current release of our packages, it still shows up in "Required by" because it is used in older releases. This makes the "Required by"-info useless for us, because we are only interested in the "Required by"-info for a specific (in our case the latest) tag/branch.

**Describe the solution you'd like**
Show the package information based on tags/branches, similar to what packagist.org does with the tag-selection:


**Describe alternatives you've considered**
The alternative is to delete old branches/tags, so that Satis will not pick up information from "composer.json"-files in old/unused tags/branches.

This approach is cumbersome, since one always has to remember to delete old tags.

**Additional context**

I can create a PR if you (package maintainers) consider this a useful feature.

No files or tests are identified in the issue. Start by tracing how Satis gathers package information across repository tags and branches, then compare the requested behavior with Packagist's tag selection. Done means package information, including "Required by" data, can be viewed for a selected tag or branch rather than all refs.

Written by the indexing model from the issue text.