test_runner: automatically rerun flaky tests (#3880)

This PR adds a plugin that automatically reruns (up to 3 times) flaky
tests. Internally, it uses data from `TEST_RESULT_CONNSTR` database and
`pytest-rerunfailures` plugin.

As the first approximation we consider the test flaky if it has failed on 
the main branch in the last 10 days.

Flaky tests are fetched by `scripts/flaky_tests.py` script (it's
possible to use it in a standalone mode to learn which tests are flaky),
stored to a JSON file, and then the file is passed to the pytest plugin.

.github/workflows/build_and_test.yml

@@ -335,6 +335,9 @@ jobs:
           real_s3_region: us-west-2
           real_s3_access_key_id: "${{ secrets.AWS_ACCESS_KEY_ID_CI_TESTS_S3 }}"
           real_s3_secret_access_key: "${{ secrets.AWS_SECRET_ACCESS_KEY_CI_TESTS_S3 }}"
+          rerun_flaky: true
+        env:
+          TEST_RESULT_CONNSTR: ${{ secrets.REGRESS_TEST_RESULT_CONNSTR }}
 
       - name: Merge and upload coverage data
         if: matrix.build_type == 'debug'