Add some QoL improvements to `Repository` admin

[joshuadavidthomas]

• Search by:
  • Repository name
  • Owner name
• Add list filters for:
  • Installation (dropdown? or just a simple list filter? would be dependent on the number of installations I guess!)
  • Owner name
• Add more fields to list table:
  • Full name -> Owner and Repository names
  • Installation account name (not just ID)
• Link to GitHub repository on list and change form
• Recent events on change form (last 10?)