docs: site: add guide for setting up Pinniped with high availability, redundancy and best practices for scalability

[Dentrax]

Is your feature request related to a problem? Please describe.

I'd be great to have a guidance on configuring Pinniped for high availability at scale. There might be challenges when setting up features like leader election, multi-supervisor support, and multi-data center (multi-DC/Region/Zone) configurations without comprehensive documentation.

Providing this information will help the users confidently deploy in production environments with resiliency and reliability in mind.

Describe the solution you'd like

Create a new document that provides:

• High Availability
  • Instructions for enabling leader election (if supported, if not - why? any ongoing plans?)
  • Recommended configurations for redundancy and fail-over
  • How many supervisors are recommended to run at scale (How many Pods / Clusters)
• Scalability best practices
  • Fine-tune configurations to optimize performance for large-scale deployments (i.e, multi-supervisors with thousands of concierges)
  • Any known limitations or suggested tuning parameters?
• Other recommendations
  • Highlight additional/important configurations or tools
  • Address common questions (in the issues) with a FAQ?
• Extra: Multi-Cluster/DC/Region/Zone Setup:
  • Steps to configure Pinniped Supervisor for multiple clusters (for H/A) - (not per-cluster)
  • Guidance on certificate management for multi-dc usage?
  • Clarify if centralized login is possible across data centers (i.e., single login for eu-west and us-central)

I've read the demo doc but I have some suspects if it covers the some open-questions or concerns above.

Describe alternatives you've considered

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Are you considering submitting a PR for this feature?

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Additional context

Include any insights into areas users frequently overlook or struggle with when deploying Pinniped at scale. Ensure documentation is concise and user-friendly.

Sorry if this seems a bit overwhelming due to the many questions. As a new user, I’d like to clarify things before actual usage. I’m happy to simplify if there’s too much context. Thank you!

/cc @developer-guy