revert leaving optional for required init fields

[lsviben]

Description of your changes

Related to crossplane-contrib/provider-upjet-gcp#355 .

In #237, the required fields in spec.forProvider were set as optional due to them being replacable by the fields in spec.initProvider (just the fields that are in spec.initProvider not all required fields like identifiers).

This also added, or rather didnt remove, the omitempty json tag for those fields. This causes boolean fields to not be properly late-initialized, which in turn causes the resource to be stuck in Synced: FALSE status as it does not have all the required fields.

So this PR reverts the change in which the omitempty tag was not being removed for fields that are required && initProvider field. Instead it removes the omitempty for all fields that are required.

Fixes #

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

How has this code been tested

Ran make generate on provider-gcp and tested running locally with a kind cluster.

The resource created is the cluster from the bug issue: crossplane-contrib/provider-upjet-gcp#355 (comment)

apiVersion: container.gcp.upbound.io/v1beta1
kind: Cluster
metadata:
  annotations:
    meta.upbound.io/example-id: container/v1beta1/cluster
  labels:
    testing.upbound.io/example-name: cluster
  name: cluster
spec:
  forProvider:
    location: europe-north1
    ipAllocationPolicy:
      - {}
    enableAutopilot: true

The result is:

kubectl get -f cluster.yaml 
NAME      READY   SYNCED   EXTERNAL-NAME   AGE
cluster   True    True     cluster         89m

[turkenh]

Thanks @lsviben 💪

[lsviben]

@ulucinar @sergenyalcin

would adding a label according to Added backport release-x.y labels to auto-backport this PR if necessary. work in this repo? Ideally this would be backported and then patched to the provider releases

[haarchri]

LGTM