Make default metadata, labels and tags optional

[kevang]

SUMMARY
A number of default tags, metadata and labels are added to the nodepools by the different modules. This is fine when creating a new nodepool, but can be problematic when importing an existing nodepool that does not have those, as a new plan will lead to nodepool recreation, for example:

~ labels            = { # forces replacement
     + "cluster_name" = "cluster-somename-9965"
     + "node_pool"    = "basic-pool"
}

PROPOSED CHANGE
The proposed change makes it possible to use the modules with existing gke clusters/nodepools. It's not introducing any breaking changes and was tested with the beta private cluster. I'm happy to update the other modules, if you think the change makes sense.

[morgante]

@kevang Please update this in the configuration in autogen/ then use make generate.

[kevang]

Thanks @morgante, I updated it (not sure if I needed to reformat the generated files, cause is seems that a couple of lines have changed and the build is failing)

[morgante]

Thanks for the contribution!

[morgante]

Looks like tests/linting is failing. Can you make sure they pass locally?

[kevang]

I reformatted and the linting tests all pass, yet I still get Error: The following tests have failed: check_documentation. I tried make docker_generate_docs but it doesn't seem to make any changes, not sure if there's anything else I'm missing

[morgante]

@kevang Looks like the linters are passing now, just waiting for integration tests to pass before merging.

[kevang]

@morgante do you think that it's ok to merge now that the checks have passed? 🙂