Fixes #3833

Up to this point we didn't specifically set tombstone_gc mode in tests and expected it to be 'timeout'. Since tablet tables need to have tombstone_gc 'repair', we should change the default expectation to it.
Note that this 'assumption' should be removed in the future in favor of something more robust.

Ent Scylla versions contain additional table "dicts" which cannot be found in OSS Scylla,
so it should be excluded when comparing GetTarget output with golden files.

ValidateTable was introduced as a workaround for errors encountered from COUNT(*), but it is no longer needed.
This commit also introduces slight groundwork needed for improved restore test framework.

TestHelper is a reimplementation of restoreTestHelper which wasn't well-designed. It removes a lot of boilerplate from test setup and also allows for more flexibility.

This test was previously failing because it's not possible to create non replicated table with tombstone_gc mode repair. This is a good opportunity to use new testHelper framework.

Starting with Scylla 6.0, system_auth is moved to system/system_auth_v2 and is handled by raft.
New clusters won't have the old system_auth tables, so the tests should be adjusted accordingly.

This test stops and starts Scylla service on a node, and it could happen that this node is not fully responsive when the next test is already running. Running this test at the end removes the races between service start and next test execution.