generate: subcommands should only require `pkg/apis` exist, not full project

[estroz]

Feature Request

Is your feature request related to a problem? Please describe.
I want to run operator-sdk generate subcommands on pkg/apis on a project without cmd/manager/main.go or build/Dockerfile. Neither of these are required to generate code for my APIs in any case.

Describe the solution you'd like
Remove project structure checks, and instead ensure pkg/apis exists instead, which should only exist in Go projects.

/cc @joelanford @hasbro17 @theishshah @fabianvf @jmrodri

[camilamacedo86]

HI @estroz,

As described in the comment #2054 (comment) was decided not to move forward with this request. The reason for that is because we are looking for to design changes to give more flexibility to our users. Then, for customizations like this one, we would like to suggest the usage of controller-gen directly by a Makefile. Following an example of a Makefile with targets to generate/update the CRD's in the SDK structure.

# Produce CRDs that work back to Kubernetes 1.11 (no version conversion)
CRD_OPTIONS ?= "crd:trivialVersions=true"

# Get the currently used golang install path (in GOPATH/bin, unless GOBIN is set)
ifeq (,$(shell go env GOBIN))
GOBIN=$(shell go env GOPATH)/bin
else
GOBIN=$(shell go env GOBIN)
endif

# Generate manifests e.g. CRD, RBAC etc.
manifests: controller-gen
	$(CONTROLLER_GEN) paths=./... crd:trivialVersions=true output:crd:artifacts:config=deploy/crds

# find or download controller-gen
# download controller-gen if necessary
controller-gen:
ifeq (, $(shell which controller-gen))
	go get sigs.k8s.io/controller-tools/cmd/controller-gen@v0.2.0
CONTROLLER_GEN=$(GOBIN)/controller-gen
else
CONTROLLER_GEN=$(shell which controller-gen)
endif

Then, when the command make manifests be called the CRD's in the path deploy/crds will be created/updated.

For further information about how to use the controller-gen options/commands see its [docs]
(https://book.kubebuilder.io/reference/controller-gen.html).