docs: document RHDP wrapper deployment path and configurable secrets locations

[butler54]

The coco-pattern getting-started guide (content/patterns/coco-pattern/coco-pattern-getting-started.adoc in validatedpatterns/docs) and Azure requirements page (coco-pattern-azure-requirements.adoc) don't currently mention the rhdp/ wrapper scripts (rhdp/wrapper.sh, rhdp/wrapper-multicluster.sh, rhdp/wrapper-cluster-only.sh) at all, even though they're the recommended, opinionated Azure deployment path (see #59's comment thread: "inside the repo is a folder called rhdp. That (for our tech sellers) provides an opinionated path to complete deployment that is stable... That wrapper script is probably the best place to understand the deployment process").

As of #130, these wrapper scripts also support:

• Overriding the OpenShift pull secret location via PULL_SECRET (env var) or --pull-secret (CLI flag on rhdp/rhdp-cluster-define.py), instead of requiring ~/pull-secret.json.
• Overriding the SSH public key location via SSH_PUBLIC_KEY (env var) or --ssh-public-key, with auto-detection preferring ~/.ssh/id_ed25519.pub, then id_ecdsa.pub, then id_rsa.pub if no override is given (previously hardcoded to ~/.ssh/id_rsa).

Requesting (to be raised against validatedpatterns/docs once someone picks this up, or done as a docs-site PR directly):

1. A short pointer/section introducing the RHDP wrapper scripts as a supported, opinionated Azure deployment path (linking to rhdp/README.md in this repo for full details).
2. Documentation of the pull-secret/SSH-key override behavior and the new Ed25519-preferred default.

This is scoped narrowly to the above — see #120 for the broader documentation overhaul (bare-metal onboarding, mixed TEE types), which is a separate, larger effort.

(Originally filed against validatedpatterns/docs as #728; moved here per maintainer preference to keep coco-pattern documentation tracking in this repo.)