Replace functional tests with Linearizability

[serathius]

What would you like to be added?

When linearizability tests reach feature parity we no longer will need functional tests. As was discussed in #14820, functional tests serve the same purpose however don't use e2e framework resulting in large maintanance code. This PR will track remaining features that we want to migrate to linearizability tests.

Property	Functional tests	Linearizability test
Cluster setup	Single global config supported. Only 3 node cluster is tested	Any number of configs. Any config supported by e2e tests
Failures	Supports process termination, network termination, supports waiting for snapshot trigger	Supports process termination, network termination, predefined failpoints. Doesn't support waiting for snapshot
Traffic	Supports writes (small and large), reads on single key and range, transaction that writes or deletes	Supports single key operations, transactions and leases
Checkers	Checks consistency of hashes	Validates linearizability which is much stricter than hashes
Max clients/QPS	100 clients generating 2000qps (not measured)	8 clients generating 200 qps

To implement in linearizability tests:

• Implement waiting for snapshot trigger in failpoints. (tests linearizability: trigger snapshot related failpoints #15104)
• Increase max QPS to at least 1000 (Reproduce issue 13766 in linearizability tests #14682)
• Support large writes (tests: Implement LargePut requests #15180)

cc @ahrtr @ptabor

Why is this needed?

Reduce maintenance code, increase simplicity.

[serathius]

We have implemented blackholing till snapshot, however we cannot enable it by default because we found an issue #15271.

With again linearizability tests finding issue that functional tests missed. Based on that I think we can proceed with removal of functional tests.