Add "interpolate" command to operator

[jandubois]

Is your feature request related to a problem? Please describe.

We need to write tests for the template logic in kubecf: cloudfoundry-incubator/kubecf#1306

For this we need to render the helm template, and then apply all generated ops files against the deployment manifest. Once we have the final manifest, we can verify that it contains the expected settings (and has removed the ones we expect to be removed).

We have some code that uses bosh interpolate in an unrelated script, that we could use for now, but that does not support the additional qcopy and qmove ops that are specific to quarks-operator.

Describe the solution you'd like

I would like the have an interpolate subcommand in the operator, and quarks releases to include operator executables compiled for both Linux and macOS that can be downloaded from the Github releases pages.

Describe alternatives you've considered

@mook-as has written his personal tool that essentially does the same: https://github.com/mook-as/go-patch-cmd

We could use that, but would prefer to use the operator binary to make sure we are using the exact same code that will be used to generate the manifest at runtime.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/174721877

The labels on this github issue will be updated when the story is started.

[jandubois]

I've just had some ideas how we can manipulate the manifest directly from the kubecf helm chart instead of using qmove/qcopy ops. If that works out, then we can continue to use bosh interpolate and won't need this feature from the operator.

[jandubois]

This is no longer required; kubecf will not make use of the qcopy/qmove ops but manipulate the deployment manifest directly.

This also means that the changes from #913 could be reverted, but that would probably be just busy-work without providing any value.