feat: Show amount of images of people on explore and people page

[didekoning]

Description

Added the number of images with a persons face to the API. The Explore and People pages will show the number next to the face thumbnail. This is based on this discussion: #5926. This also fixes a bug in the getAllForUser repository where duplicate assets where also counted and used for sorting.

This makes it easier to see how many images there are of a person.

Fixes # 5926

How Has This Been Tested?

• Manual tests with large numbers
• Added Unit tests
• Added integration test

Screenshots (if appropriate)

Explore page:

People page:

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation if applicable
• I have no unrelated changes in the PR.
• I have confirmed that any new dependencies are strictly necessary.
• I have written tests for new code (if applicable)
• I have followed naming conventions/patterns in the surrounding code
• All code in src/services/ uses repositories implementations for database calls, filesystem operations, etc.
• All code in src/repositories/ is pretty basic/simple and does not have any immich specific logic (that belongs in src/services/)

Please describe to which degree, if any, an LLM was used in creating this pull request.

For some initial setup only.
...

[immich-push-o-matic]

Label error. Requires exactly 1 of: changelog:.*. Found: 🖥️web, 🗄️server. A maintainer will add the required label.