Add Manual Refresh Button for Linked Repositories/Issues/PRs, filters, and contributors list for GH integration

### Is your feature request related to a problem? Please describe.

- It might be beneficial to have a manual 'Refresh Repositories' button next to the dropdown when linking a repository. Currently, adding a repository on the GitHub side requires a hard refresh of the page before it is picked up in Flagsmith.

- Enhance the GitHub integration by implementing filters and a contributors list. These would improve the user experience by allowing users to navigate through repositories easily.
### Describe the solution you'd like.

Add a "refresh" icon/button next to the list that forces an update.
Add filters above or next to the select for a more advanced search of issues and pull requests.

### Describe alternatives you've considered

Refreshing the entire Flagsmith dashboard UI works but is a hack.

### Additional context

_No response_