Information about RH-SSO caches have disappeared from RH-SSO 7.6 doc

Issue description

Information related to caches has disappeared from the RH-SSO 7.6  documentation.

Caches are still in use with RH-SSO, but only used as embedded caches to perform RH-SSO clustering.

Before, those caches Information were described within the RH-SSO installation guide (section Cross DC which has been removed since) .

What is needed:
1. It is ** needed to describe those ** 7 caches as it was done previously (and even improving the explanation - Why not )

2. Explain also the command which enable/ disable caching (for users/ realms ...)

<distributed-cache name="sessions" owners="1">
                    <expiration lifespan="900000000000000000"/>
                </distributed-cache>
                <distributed-cache name="authenticationSessions" owners="1">
                    <expiration lifespan="900000000000000000"/>
                </distributed-cache>
                <distributed-cache name="offlineSessions" owners="1">
                    <expiration lifespan="900000000000000000"/>
                </distributed-cache>
                <distributed-cache name="clientSessions" owners="1">
                    <expiration lifespan="900000000000000000"/>
                </distributed-cache>
                <distributed-cache name="offlineClientSessions" owners="1">
                    <expiration lifespan="900000000000000000"/>
                </distributed-cache>
                <distributed-cache name="loginFailures" owners="1">
                    <expiration lifespan="900000000000000000"/>
                </distributed-cache>
                <distributed-cache name="actionTokens" owners="2">
                    <heap-memory size="-1"/>

3. A good placeholder could be to add a section "Using Caches" within the Clustering section of the RH-SSO documentation, as caches are tightly realted to clustering.