fix: Use environment variables for agent authentication (#1238)

* 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!

cli/config/file.go

@@ -21,10 +21,6 @@ func (r Root) Organization() File {
 	return File(filepath.Join(string(r), "organization"))
 }
 
-func (r Root) AgentSession() File {
-	return File(filepath.Join(string(r), "agentsession"))
-}
-
 // File provides convenience methods for interacting with *os.File.
 type File string