CDAP-19300 adding container injection feature and Dockerfile for unit testing on Docker image

[mariogiuffrida]

This change refers to the ticket CDAP-19300 - https://cdap.atlassian.net/browse/CDAP-19300.

In this change, we introduced:

• the possibility of injecting containers inside Stateful and Deployment services.
• the possibility to override the service ports (i.e. router listening on non-default ports)
• a new Dockerfile.test specifically used to run unit test on a Docker image

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[mariogiuffrida]

Thank you @dli357 I have now uploaded a new commit version

[mariogiuffrida]

Thank you for all your great feedback @arjan-bal! I have now uploaded a new commit version.

[mariogiuffrida]

@arjan-bal @dli357 I have uploaded a new version which considers all your comments (thank you). Could you please review it?