The goal of the script is to assist with removing changelog entries that
are already included into a release of another development branch.

For example, if a bug fix is released as part of 2.11.3, there is no
reason to highlight that it is fixed in 3.0.0. It is better to describe
changes comparing to the latest present 2.11 release.

The script was initially written for personal use and there are obvious
points for improvements. However, it seems that it already simplifies
some tasks, so I'm going to share it as is and improve later. I'll leave
the relevant issue open.

Part of #9135

NO_DOC=The commit adds a development tool and doesn't touch anything in
       tarantool itself.
NO_CHANGELOG=see NO_DOC
NO_TEST=see NO_DOC