feat: Add username to generated branch name

Description

This resolves Default branch names in the Web IDE should incl... (gitlab#387402 - closed) by adding a

Screenshot

Before	After

How to test

With the example app:

• Start the example app yarn start:example.
• Visit the example app URL and add the query param /?username=loremipsum to the URL.
• Enter the Client Only config params and be sure to include an access token.
• In the Web IDE, make a change to any file to enable committing in the source control.
• In the Web IDE, click the source control tab and click the dropdown next to "Commit to ..." and click "Commit to new branch"
• Assert: The generated branch name should start with loremipsum-.

Thanks

Thanks to @erran @jtapiab @ahmed.hemdan for pairing on this with me!