start browser in a new thread and point directly to the dashboard

[alexpasmantier]

• I have added an entry to CHANGELOG.md, or an entry is not needed for this change

Summary of changes

This fixes somewhat of a "bug", where on first launch the browser will regularly open http://127.0.0.1:5000 and display an "Unable to connect" error.

I'm assuming this is because the browser is launched by the main thread in a state where the server hasn't had enough time to initialize and serve the page in question.

This PR just moves that to another thread to both speed up server initialization and avoid the error altogether.

Test plan

Tested by running

# command(s) to exercise these changes

Running the gui locally