Catalina support

Updated contrib/googletest to v1.10.0

Refactor changelog

Much comprehensive documentation

Port changes from #8545 to processors.

Fix substring negative size

Report a more verbose error when unable to select parts to merge.

<filesystem> support was only introduced in Mac OS 10.15: minimum version must be raised to compile on Catalina

Fix mutation size limit

check for active replicas when waiting for commands

try fix some predicate optimizer bug

Removed useless code, added comments

fix typo in tutorial.md

Increased number of rows to make tests results noticeable.

Processors 5.8

Update apply_catboost_model.md

PolicyInfo::setPolicy() now doesn't throw an excepion on empty filter.

replace ant with want (forgotten w)

ensure network be up

Update security changelog

This reverts commit 84bc2bd1.