Differentiate and Filter Translations by User Group (e.g., Community vs. LSP)

### Describe the problem

We work with two distinct translator groups: a professional Language Service Provider (LSP) and volunteer community translators. Currently, Weblate does not provide a way to differentiate contributions from these groups. This makes it difficult to apply separate Quality Assurance (QA) workflows or accurately track contributions from each source.

### Solution brainstorm

We propose a feature based on User Groups.
- When a user from a specific group (e.g., the 'LSP' group) saves a translation, store the user's group as metadata associated with that specific string version.
- Enhance the search and filtering capabilities to allow users to filter strings based on the translator's group (e.g., "Show all strings last edited by the 'Community' group").

### Describe alternatives you have considered

_No response_

### Screenshots

_No response_

### Additional context

Key Benefits
This would enable several improvements to our workflow:
- We could quickly filter and batch-approve all work from the trusted LSP group.
- We could easily isolate community translations to send them for professional review.
- We could track and report on community contributions to acknowledge their valuable work.

This would make our review process much more efficient and give us better insight into our localization efforts.