Ensure GVK is properly detected

[patrickdappollonio]

Description

There's a tiny little issue in the current code: since we're unsafely generating the pluralized version (used in internal Kubernetes URLs) to apply manifests, if we get an object like kind: NetworkPolicy, we "pluralize" it for the server as "networkpolicy" + "s":

colony/internal/k8s/k8s.go

Line 97 in 2f990e5

Resource: strings.ToLower(gvk.Kind) + "s",

This PR adds a REST unstructured mapper that can map specific objects by asking the Kubernetes API if it knows them.

Today we don't store any NetworkPolicy, and fortunately enough Workflow or Template pluralizes in English correctly by adding s at the end, but that might not always be the case especially if this functions makes its way to other parts of our code.

The Unit Test includes the happy path (submitting a known resource) and the unhappy path (submitting an unknown resource). The previous error was:

Error: error applying templates: error creating resource: the server could not find the requested resource

And the new error is (using the example of not finding what a NetworkPolicy is:

Error: error applying templates: error creating resource: unable to map manifest to a Kubernetes resource: no matches for kind "NetworkPolicy" in version "networking.k8s.io/v1"

(A bit more verbose but it tells you what action was happening and why it couldn't be applied).

This PR also adds a unit test to pull from the API to ensure the response stays correct, although that could've probably been done in a different PR.

Related Issue(s)

Fixes #

How to test

go test -timeout 30s -run ^Test_ApplyManifests$ -count=1 -v ./...

[douglasmakey]

Approved. Just a small note: this function was a temporary solution until we defined the method for delivering the templates. It's just for templates and not for any other resource.