devel: add release-checks.sh

Currently Makefile.local contains some machine executable release
checking functionality. This is unnecessarily complex way to do it:

Multiline script functionality is hard to embed -- from Makefile point
of view there is just one line split using backslashes and every line
ends with ';'. It is hard to maintain such "script" when it gets longer.

The embedded script does not fail as robust as separate script; set -eu
could be added to get same level of robustness -- but the provided
Bourne Again Shell (bash) script exceeds this with 'set -o pipefail',
making the script to fail when any of the commands in pipeline fails
(and not just the last one).

Checking for release is done very seldom compared to all other use;
The whole Makefile.local gets simpler and easier to grasp when most
release checking targets are removed.

When release checking is done, the steps are executed sequentially;
nothing is allowed to be skipped due to some satisfied dependency.