Improve set security user processor doc with examples

[ywangd]

The set security user processor are being augumented to provide more information about the authenticated user (#49106) . The change will introduces new fields and some of them are objects themselves containing more fields.

The associated documentation can be improved with examples to clarify the usage and results of different configurations.

[elasticmachine]

Pinging @elastic/es-docs (>docs)

[elasticmachine]

Pinging @elastic/es-security (:Security/Authentication)