all: replace links to sourcegraph master to main

Created by: keegancsmith

Spotted a place linking to the master branch. Ended up updating all references I could find with a simple regex:

ruplacer --go '(sourcegraph/sourcegraph/[^/]+)/master/' '$1/main/'

Test Plan: CI

App preview:

• Web
• Storybook

Check out the client app preview documentation to learn more.