[DOC] Document security REST APIs

[Naarcha-AWS]

What do you want to do?

• [x] Add new documentation

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Relates to issue #530

There are 8 security APIs that are not documented. Quickly checking a subset of the APIs in security with query for BaseRestHandler shows the following gaps:

Documented	API Path	Http Verbs	Code Reference	Notes
🚫	/_plugins/_security/dashboardsinfo	GET & PUT	DashboardsInfoAction
🚫	/_plugins/_security/kibanainfo	GET & PUT	DashboardsInfoAction	should be deprecated?
🚫	/_plugins/_security/whoami	GET & POST	SecurityWhoAmIAction	No java docs
🚫	/_opendistro/_security/sslinfo	GET	SecuritySSLInfoAction
✔️	_opendistro/_security/api/ssl/{certType}/reloadcerts/	PUT	SecuritySSLReloadCertsAction	Has java documentation
🚫	/permissionsinfo	GET	PermissionsInfoAction	Internal only API?
🚫	/_plugins/_security/authinfo	GET & POST	SecurityInfoAction
🚫	/_plugins/_security/tenantinfo	GET & POST	TenantInfoAction
🚫	/_plugins/_security/configupdate	PUT	SecurityConfigUpdateAction

Do you have any related resources to help us get started?

POC: @peternied

Is there anything else you'd like to add?