feat: add extensible registry interface and integrate into config and meta-config registries

[Bloeckchengrafik]

Pull Request

Description

As discussed via discord: Provides a way to extend the "search radius" of the pack and metapack registres using 4 system properties documented in the code below

Changelog

• Allow specifying extra search paths for packs and metapacks

Checklist

Mandatory checks

• The base branch of this PR is an unreleased version branch (that has a ver/ prefix)
  or is a branch that is intended to be merged into a version branch.
• There are no already existing PRs that provide the same changes.
• The PR is within the scope of Terra (i.e. is something a configurable terrain generator should be doing).
• Changes follow the code style for this project.
• I have read the CONTRIBUTING.md
  document in the root of the git repository.
• LLM-based tools were not used to create this PR. (ChatGPT, Claude, etc)

Types of changes

• Bug Fix
• Build system
• Documentation
• New Feature
• Performance
• Refactoring
• Repository
• Revert
• Style
• Tests
• Translation

Compatibility

• Introduces a breaking change
• Introduces new functionality in a backwards compatible way.
• Introduces bug fixes

Documentation

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
  • TODO

Testing

• I have added tests to cover my changes.
• All new and existing tests passed.

Licensing

• I am the original author of this code, and I am willing to
  release it under GPLv3.
• I am not the original author of this code, but it is in public domain or
  released under GPLv3 or a compatible license.

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This does not build

This does not build due to missing stuff in the 1.21.11 branch.
Minestom part published
https://mvn.everbuild.org/#/public/com/dfsek/terra/minestom/7.0.0-BETA+b49b38f24

[solonovamax]

should the concept of extending a registry maybe be abstracted a bit, so it can be extended both via system properties, but also by different providers? (config file, env variable, cli param, etc.)

[Bloeckchengrafik]

Sorry I haven't got around to this earlier. Review comments are adressed.

Built: https://mvn.everbuild.org/#/public/com/dfsek/terra/minestom/7.0.0-BETA+47b17b1e0