Allow local connections to cable when in dev env

What does this MR do and why?

The MR adds 127.0.0.1 and gdk.test to allowed origins when connecting to ActionCable in dev environment. This allows testing WebSocket connections in the local Web IDE + Duo Chat instances.

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⚠ nevermind the "error" respond from chat - it's irrelevant to this MR

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Related to gitlab-vscode-extension#1219 (closed) and #432723 (closed)