GitHub Integration - Link to closed issues / PRs

### How are you running Flagsmith

- [ ] Self Hosted with Docker
- [ ] Self Hosted with Kubernetes
- [X] SaaS at flagsmith.com
- [ ] Some other way (add details in description below)

### Describe the bug

When trying to associate our flags with GH issues I found that I couldn't

### Steps To Reproduce

Attempt to find "Add meta data fields to core entities"

### Expected behavior

- I can link the feature
- With a lot of features it might be difficult to find the right one, searching for #id would be ideal
- We should be able to see an indication of whether the issue / PR is closed/open

### Screenshots