Document Omni break glass flag

Need to talk about:
* What it's for (Omni outage direct access). 
* How to enable it (`--enable-break-glass`?) flag for self-hosted or open an issue for the SaaS
* What it provides `os:operator` credentials to Talos and Kubernetes

Downsides:
* Doesn't work in maintenance mode (still protected with siderolink)
* Credentials don't expire (I'm not sure how you can rotate the credentials)