fix(core): Improving typing for common container usage scenarios

[santi]

Improves type hints for type checking in a common use cases:

with MySqlContainer("mysql:8").with_env("some", "value") as mysql:
    url = mysql.get_connection_url()  # get_connection_url would previously be an unknown member here

And, also improved type hinting for the custom DockerClient's run command, where the linter no longer reports an error due to missing parameter types:

DockerClient.run("nginx")  # Previously this would report "Argument missing for parameter "image"

[alexanderankin]

linking #504 and #305