CI: valgrind tests

[sanikolaev]

Let's add nightly Valgrind tests, similar to how it's done in https://github.com/manticoresoftware/manticoresearch.

[sanikolaev]

Let’s first make sure it works in manual mode.
@klirichek, could you adapt https://github.com/manticoresoftware/manticoresearch/blob/master/memcheck.sh for this repo and check that it works correctly?