Add loading indicator to issue search
If you're searching through the issue list on the thread details, we currently don't display a loading indicator, which can be frustrating as the search is slow often and it appears that Productlane isn't working.
[Loading - Tool (Figma)](https://www.figma.com/design/L3JTxZAPRVvjyEaqFiXZin/Tool?node-id=17290-3500&node-type=FRAME&t=ojg28qA3QybyI5gY-11)
![image.png](https://uploads.linear.app/922eb553-8dc5-4a00-a16b-01735334be53/e6efa21d-ba52-422c-b526-c56386c380be/519b423e-cb91-4064-827b-9d123b10fd7b)