[WIP] Add command args to container creation

[CodingParsley]

Description

It provides lightweight solution to run some easy startup commands before running druid script For example, for debugging purpose if we want to check if an environment variable has been set before the druid script was run, we can set

startScript: sh
entryArg: echo ${ENV} >> file

The container will run sh -c "echo ${ENV} >> file && /bin/run-druid.sh {nodetype}

Another example use case is that if we need to source a file before running the druid script, it provides a lightweight solution to do that - we can set

startScript: sh
entryArg: source ${filename}

And the container will run sh -c "source ${filename} && /bin/run-druid.sh {nodetype}

If entryArg is not set, the container will act the same as before, thus preserving backward compatibility. The PR also added variable druidScript to customize druid script path.

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This PR has:

• [x] been tested on a real K8S cluster to ensure creation of a brand new Druid cluster works.
• [x] been tested for backward compatibility on a real K*S cluster by applying the changes introduced here on an existing Druid cluster. If there are any backward incompatible changes then they have been noted in the PR description.
• [x] added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• [x] added documentation for new or modified features or behaviors.

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Key changed/added files in this PR

• entryArg
• druidScript

[CodingParsley]

@AdheipSingh Thank you ❤️

[AdheipSingh]

@AdheipSingh Thank you ❤️

ill run this locally and test, cc @nishantmonu51 for approval to run CI.

just a question, does this PR work if you specify image for all nodeSpecs and also for individual nodeSpec ?

[AdheipSingh]

@xvrl can you approve this PR to run the CI. :)

[CodingParsley]

just a question, does this PR work if you specify image for all nodeSpecs and also for individual nodeSpec ?

Yes, this PR does not change the image of the container

[CodingParsley]

@xvrl Maybe another look? 🙏