Remove Repositories::TreeFinder inheritance

What does this MR do and why?

Repositories::TreeFinder was previously inheriting from GitRefFinder, however, on inspection of the logic I found that the inherited logic is never used except for the attr_accessors and the initializer

Describe in detail what your merge request does and why.

1. Removes parent class GitRefFinder from Repositories::TreeFinder
2. Adds attr_accessor for :params
3. Delegates repository to user_project

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Make the FlightJS/flight project public

     project = Project.find_by_full_path('flightjs/flight')
     project.id => 6 # if this is not 6 you will need to update the curl command below
     project.update visibility_level: Project::PUBLIC

2. Query the api endpoint for listing repo trees

     curl http://gdk.test:3000/api/v4/projects/6/repository/tree
     curl http://gdk.test:3000/api/v4/projects/6/repository/tree?recursive=true
     curl http://gdk.test:3000/api/v4/projects/6/repository/tree?recursive=true&path=doc
     curl http://gdk.test:3000/api/v4/projects/6/repository/tree?ref=trigger-hook

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.