[BUG][Tiered cache] Removal on EhcacheDiskCache key iterator doesn't work

[sgup432]

Describe the bug

EhcacheDiskCache exposes a way to iterator over keys which is basically a wrapper over underlying ehcache iterator. Link

If we try to call iterator.remove() on above iterator, it won't work as it isn't supported.

Related component

Search:Performance

To Reproduce

Write a simple unit test on EhcacheDiskCacheTests, fetch iterator and call remove(). Try to assert that the key actually got removed.

Expected behavior

Calling remove() on EhCacheKeyIterator should be able to remove the desired key.

For fix, we need to override remove() in above class.

Additional Details

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[sgup432]

@sohami @kiranprakash154