Added standalone job with coverity check as described at [1]. This
job uploads results to coverity.com host to 'tarantool' project when
COVERITY_TOKEN environment is enabled. Main coverity functionality
added at .travis.mk make file as standalone targets:

  'test_coverity_debian_no_deps' - used in github-ci actions
  'coverity_debian' - additional target with needed tools check

This job configured by cron scheduler on each Saturday 04:00 am.

Closes #5600

[1] - https://scan.coverity.com/download?tab=cxx