* fix: Update GIT_COMMITTER_NAME to use username
This was a mistake when adding the committer fields 🤦.
* fix: Use environment variables for agent authentication
Using files led to situations where running "coder server --dev" would
break `gitssh`. This is applicable in a production environment too. Users
should be able to log into another Coder deployment from their workspace.
Users can still set "CODER_URL" if they'd like with agent env vars!
