feat: Add keep-null-value-keys parameter (Issue #780)

[gzub-resonate]

Issue 780 - Add parameter to keep null or empty keys in taskdef

Added a new parameter called keep-null-value-keys which allows you to provide a csv separated list of keys which should not be dropped if they are empty, this is important for elements that have default values which are populated and you want to override them in the taskdef.

In our particular use case we wanted to override the tag parameter to be an empty string as in the splunk logging driver it defaults to a value "{{.ID}}", because of this default and the dropping of empty values this was not possible in the current version.

I added additional unit tests and verified that this action exhibits the correct behavior in our workflow.

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[gzub-resonate]

Any update on when this might get reviewed?

[gzub-resonate]

Can I get some more guidance on what is needed to help move this along... thanks!

[djglaser]

Hi @gzub-resonate, thank you for opening this PR. Our team will review it. In the meantime, can you please fix the failing build checks? Thank you!