Update Documentation about CAS Authentication

[bnasslahsen]

Describe the bug
The class org.springframework.security.cas.authentication.EhCacheBasedTicketCache has been removed in spring-security 6.x but is still referenced in the documentation.

To Reproduce
Go to https://docs.spring.io/spring-security/reference/servlet/authentication/cas.html#cas-pt and look for EhCacheBasedTicketCache.
EhCacheBasedTicketCache was deprecated in spring-security 5.6, then removed in spring-security 6.x.

This is the link for the github doccumentation:

spring-security/docs/modules/ROOT/pages/servlet/authentication/cas.adoc

Lines 451 to 463 in 2455feb

	<bean class="org.springframework.security.cas.authentication.EhCacheBasedTicketCache">
	<property name="cache">
	<bean class="net.sf.ehcache.Cache"
	init-method="initialise" destroy-method="dispose">
	<constructor-arg value="casTickets"/>
	<constructor-arg value="50"/>
	<constructor-arg value="true"/>
	<constructor-arg value="false"/>
	<constructor-arg value="3600"/>
	<constructor-arg value="900"/>
	</bean>
	</property>
	</bean>

Expected behavior
I believe the documentation can be updated to use SpringCacheBasedTicketCache instead.