[v9_16] Add "stress" tests to GitLab CI
Run "stress" tests for scheduled pipelines and pipelines created for tags. These tests were previously only performed manually (as part of pre-release testing of each new BIND version). Their purpose is to detect memory leaks and potential performance issues.
As the run time of each "stress" test itself is set to 1 hour, set the GitLab CI job timeout to 2 hours in order to account for the extra time needed to set the test up and gather its results.
(cherry picked from commit 39305411)