Adds security_index info to endpoint docs

[spacether]

• Adds security_index info to endpoint docs
• Adds allowed values for security_index and server_index
• Fix: corrects the link to the root server info from endpoint docs
• makes servers a required key in server_index_info and security_index_info
• Adds codes sample for security_index_info if there is more than one security

The fact that the docs needed this info came up in: #180

PR checklist

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