Log script change/add and removal at INFO level

Closes #6104
Significant_terms agg: added option for a background_filter to define background context for analysis of term frequencies

Closes #5944
[DOCS] Fix typos in context suggest
Use t-digest as a dependency.

Our improvements to t-digest have been pushed upstream and t-digest also got
some additional nice improvements around memory usage and speedups of quantile
estimation. So it makes sense to use it as a dependency now.

This also allows to remove the test dependency on Apache Mahout.

Close #6142
[TEST] Changed the possessive matching syntax in cat.recovery
regex to use an independent subexpression. Possessive
modifiers not supported on older Perl
[DOCS] Changed coming[1.1.0] to added in snapshot status
[JAVADOCS] Fix wrong javadoc in IdentityHashSet.

Close #6121
[TEST] Ensure no bechmarks are running after test
Report all errors if benchmark fails and mark as failed
Log cache recycler clear call as debug
Read full message on free context

Since #5730 we write a boolean in the FreeContextResponse which should be deserialized

Closes #6147