feat: allow TESTCONTAINERS_HOST_OVERRIDE to override docker host

[Hugoch]

This PR adds the option to customize Docker hostname detection with the TESTCONTAINERS_HOST_OVERRIDE environment variable.
It replicates the behavior of the Java testcontainer package (https://java.testcontainers.org/features/configuration/)

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[DDtKey]

Thank you for the contribution!

[DDtKey]

There is more appropriate place for this - it should be part of the config

Moreover config already has tc_host which is prioritized, but we read it only from properties file.
What we can do is to extend this part and read tc_host from env variables too

testcontainers-rs/testcontainers/src/core/env/config.rs

Lines 103 to 119 in d652b38

	async fn load_from_env_config<E>() -> Result<Self, ConfigurationError>
	where
	E: GetEnvValue,
	{
	let host = E::get_env_value("DOCKER_HOST");
	let tls_verify = E::get_env_value("DOCKER_TLS_VERIFY").map(|v| v == "1");
	let cert_path = E::get_env_value("DOCKER_CERT_PATH").map(PathBuf::from);
	let command = E::get_env_value("TESTCONTAINERS_COMMAND")
	.filter(|v| !v.trim().is_empty())
	.map(|v| v.parse())
	.transpose()?;
	let docker_auth_config = read_docker_auth_config::<E>().await;
	Ok(Config {
	host,
	tc_host: None,

[Hugoch]

Thanks for the feedback @DDtKey ! The issue here is that tc_host and docker_host() are used to resolve the Docker host for both connecting to Docker socket/server and to resolve URLs for containers. For example in the case of Docker on Mac, Docker socket is correctly resolved but we need the host for container addresses to be resolved as host.docker.internal instead of localhost. So I think those 2 variables need to be separated?

[DDtKey]

I'm not sure I got the issue you're trying to explain. tc.host exists to allow overriding the host for testcontainers only.

But main driver of my suggestion is that tc_host behaves this way in other languages, e.g in go:

    // TestcontainersHost is the address of the Testcontainers host.
    //
    // Environment variable: TESTCONTAINERS_DOCKER_SOCKET_OVERRIDE
    TestcontainersHost string `properties:"tc.host,default="`

It's a value either from TESTCONTAINERS_DOCKER_SOCKET_OVERRIDE env variable or tc.host property