Enable AsyncIO cluster mode lock

[KMilhan]

Pull Request check-list

Please make sure to review and check all of these items:

• Does $ tox pass with this change (including linting)?
• Do the CI tests pass with this change (enable it first in your forked repo and wait for the github action build to finish)? -> Couldn't configure my fork's Action -> CI here passed
• Is the new or changed code fully tested?
• Is a documentation update included (if this change modifies existing APIs, or introduces new ones)?
• Is there an example added to the examples folder (if applicable)?
• Was the change added to CHANGES file?

Description of change

Enable AsyncIO cluster mode lock. AsyncIO Cluster mode has not been providing Lock, due to the fact that the core.py trying to find the connection_pool attribute where it's not provided in the AsyncIO cluster client. This change will try to find get_encoder in the client if connection_pool is unavailable.

Also, this change copies the lock method of AsyncIO client (please let me know if this is not appropriate), providing the same API to the users whether they are using non-cluster or cluster.

An example is not added as there is no currently available cluster-mode-only example for asyncio Redis.

Closes: #2420

[codecov-commenter]

Codecov Report

Base: 92.05% // Head: 92.03% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (81a8d41) compared to base (16270e4).
Patch coverage: 72.72% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2446      +/-   ##
==========================================
- Coverage   92.05%   92.03%   -0.03%     
==========================================
  Files         110      110              
  Lines       28705    28721      +16     
==========================================
+ Hits        26425    26433       +8     
- Misses       2280     2288       +8     

Impacted Files	Coverage Δ
tests/test_asyncio/test_lock.py	100.00% <ø> (ø)
redis/commands/core.py	82.06% <50.00%> (-0.11%)	⬇️
redis/asyncio/cluster.py	90.70% <80.00%> (+0.41%)	⬆️
redis/asyncio/lock.py	99.13% <88.88%> (+0.04%)	⬆️
tests/test_cluster.py	96.85% <0.00%> (-0.24%)	⬇️
tests/test_asyncio/test_pubsub.py	99.37% <0.00%> (-0.16%)	⬇️
tests/test_asyncio/test_cluster.py	97.29% <0.00%> (-0.14%)	⬇️

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[KMilhan]

Maybe we can simplify my change by using [registered_client|redis].get_encoder() only in Async[Cluster]?
Below is from redis/asyncio/client.py

    def get_encoder(self):
        """Get the connection pool's encoder"""
        return self.connection_pool.get_encoder()

and redis/commands/core.py

    def get_encoder(self):
        """Get the encoder to encode string scripts into bytes."""
        try:
            return self.registered_client.get_encoder()
        except AttributeError:
            # DEPRECATED
            # In version <=4.1.2, this was the code we used to get the encoder.
            # However, after 4.1.2 we added support for scripting in clustered
            # redis. ClusteredRedis doesn't have a `.connection_pool` attribute
            # so we changed the Script class to use
            # `self.registered_client.get_encoder` (see above).
            # However, that is technically a breaking change, as consumers who
            # use Scripts directly might inject a `registered_client` that
            # doesn't have a `.get_encoder` field. This try/except prevents us
            # from breaking backward-compatibility. Ideally, it would be
            # removed in the next major release.
            return self.registered_client.connection_pool.get_encoder()

[dvora-h]

LGTM!