[Tiered Caching] Add additional IT tests for EhcacheDiskcache

[sgup432]

Is your feature request related to a problem? Please describe

As part of tiered caching, we added a ehcache disk cache tier to be used in additional to on heap cache. We don't have enough IT tests as we were still waiting on all changes to be merged in (like serializers etc) before we do that.

Describe the solution you'd like

Add IT test for ehcacheDiskCache following scenarios:

• Sanity testing for basic put/get.
• Test invalidation function
• Verify stats are functioning correctly.
• Verify close() is called appropriately.

Related component

Search:Performance

Describe alternatives you've considered

No response

Additional context

No response