AST fuzzer - created #43202

Integration test failures:

• test_keeper_four_word_command/test.py::test_cmd_stat - fix Fix test_keeper_four_word_command::test_cmd_stat #43115
• test_merge_tree_s3/test.py::test_table_manipulations[node]- known Integration test: thread sanitizer report on cluster shutdown #43169

There are two issues with this PR:

• SettingsRandomizer in clickhouse-test is used for functional tests, so this PR enables fault injections in functional tests (seems like it was not expected). Yes, it randomizes settings in stress tests too, but as a side effect (because stress tests just run functional tests in many threads).
• Random settings are used in BC check as well. So we have the same issue as we had in Keeper retries during insert (clean) #42607 (comment). All queries in BC check fail with Code: 115. DB::Exception: Setting insert_keeper_max_retries is neither a builtin setting nor started with the prefix 'custom_' registered for user-defined settings. (UNKNOWN_SETTING) (you can check clickhouse-server.backward.stress.log), so it tests nothing. Unfortunately, our scripts for stress tests cannot detect this automatically, so checks were green.

@tavplubix has very valid points, we have to revert this change :(