feat: add TESTCONTAINERS_HOST_OVERRIDE as alternative to TC_HOST

[meiswjn]

Resolves #383

This PR aims to unify the configuration for the Testcontainer Hostvariable as it is in Java and Dotnet (and potentially others).

[totallyzen]

I'm closing this because we've got #388 as a potential improved implementation over this. Please comment/advise based on thatissue! :pray:

[meiswjn]

Hey @totallyzen, I think this PR is not really related to #388. What I am doing is unifying environment variables (as found in every other testcontainer distribution). This line remains unchanged in the other PR: https://github.com/testcontainers/testcontainers-python/blob/5356caf2de056313a5b3f2805ed80e6a23b027a8/core/testcontainers/core/docker_client.py#L112

Would you re-consider my proposed change, please?

[alexanderankin]

reopening temporarily so it doesnt get lost