[feature] Use extra browser for Browser Steps

**Version and OS**
v0.49.15 on linux/docker

**Is your feature request related to a problem? Please describe.**
When I edit the Browser Steps for a watch, my local browser is always used (even if I manually selected an extra browser under Edit Watch > Request

**Describe the solution you'd like**
A simple drop down to let me choose the browser on the Edit Watch > Browser Steps page would be excellent. This will also let me instantly check the differences between my local browser and the extra browser.

Start at the Edit Watch > Browser Steps page and trace how the browser selected under Edit Watch > Request is currently stored and used. Follow the existing Browser Steps flow, then verify that choosing a local or extra browser changes the browser used and that both options can be compared.

Written by the indexing model from the issue text.