Additional command for container startups

[artemptushkin]

Some cases might require an additional command on the container start-up.
In general, it could be quite an often case to execute an additional command on the testcontainers start.

Currently, if we configure com.playtika.test.common.properties.CommonContainerProperties #command it will override the default command.

I would suggest adding an additional property like additionalCommands and if it is notNull pass it with withCommand:

new GenericContainer(properties.getDockerImage())
                .withExposedPorts(properties.getPort())
                .withCommand(
                        "/bin/sh",
                        "-c",
                        format(
                                "gcloud beta emulators pubsub start --project %s --host-port=%s:%d",
                                properties.getProjectId(),
                                properties.getHost(),
                                properties.getPort()
                        ),
                   additionalCommands
                )