Create a detailed How-to guide for Vault install on given infrastructure

[aurelienmaury]

Add a how-to guide for a vault installation on a user-owned infrastructure, that begins with:

ansible-galaxy collection install wescale.hashistack

and ends with:

"Validate that this url is responding."

Elements of interest:

• Preflight checklist on infrastructure, inventory and certificates, DNS records.
• Project init
• Infrastructure requirements ( ansible -m ping all -b ), even LB if needed
• Where to put certificates
• Which variables to use to point them for the playbooks to upload them
• Which DNS record to create
• Which variables to set for DNS integration

[aurelienmaury]

First version exist here: https://hashistack.readthedocs.io/en/latest/howto/deploy_onprem.html

Review and update to facilitate usage.