Add load-pkg to the makefile and add the development guide link to README

[turkenf]

Description of your changes

This PR adds load-pkg dev make target to the makefile.

Fixes: #309

I have:

• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

• Run the following command:

make load-pkg PROVIDERS="cloudplatform container" REPO="index.docker.io/turkenf"

• After the above command is completed:

> docker image ls
REPOSITORY                                 TAG                         IMAGE ID       CREATED        SIZE
turkenf/provider-family-gcp-amd64          v1.1.0-rc.0.42.g42cf069b9   baac1f7e697d   6 weeks ago    179MB
turkenf/provider-gcp-cloudplatform-amd64   v1.1.0-rc.0.42.g42cf069b9   fe2106877bf9   6 weeks ago    181MB
turkenf/provider-gcp-container-amd64       v1.1.0-rc.0.42.g42cf069b9   94f8d11c2709   6 weeks ago    181MB
turkenf/provider-gcp-cloudplatform-arm64   v1.1.0-rc.0.42.g42cf069b9   edbf18e9d01f   6 weeks ago    176MB
turkenf/provider-gcp-container-arm64       v1.1.0-rc.0.42.g42cf069b9   0d3ab205ef66   6 weeks ago    176MB
turkenf/provider-family-gcp-arm64          v1.1.0-rc.0.42.g42cf069b9   a6ef52d83555   6 weeks ago    175MB

Installable images for the family config provider created by default.

• Manually tested and installed config and cloudplatform packages in local cluster:

> kubectl get providers.pkg.crossplane.io
NAME                                 INSTALLED   HEALTHY   PACKAGE                                                                              AGE
upbound-provider-gcp-cloudplatform   True        True      index.docker.io/turkenf/provider-gcp-cloudplatform-arm64:v1.1.0-rc.0.42.g42cf069b9   115s
upbound-provider-gcp-config          True        True      index.docker.io/turkenf/provider-family-gcp-arm64:v1.1.0-rc.0.42.g42cf069b9          115s

[ulucinar]

Thanks @turkenf, lgtm. Left some comments for you to consider. As discussed offline, we may consider surfacing the XPKG_REG_ORGS Make variable as it affects the family config provider dependency generated in the resource provider's metadata and has the potential to simplify the installation step because users will not have to deal with the config provider dependency. Please see this.

[ulucinar]

Suggested change

	For building provider images locally, follow the guide [here](https://github.com/upbound/upjet/blob/main/docs/buliding-provider-images.md).
	For building provider images locally, follow the guide [here](https://github.com/upbound/upjet/blob/main/docs/building-provider-images.md).

[turkenf]

/test-examples="examples/cloudplatform/serviceaccount.yaml"

[turkenf]

/test-examples="examples/bigquery/connection.yaml"

[ulucinar]

Thank you @turkenf for improving the developer experience. Building an (installable) provider package for the provider families has been a constant confusion point for these repos. Hopefully this will simplify the process for the provider developers.

We also need to document this new target. A section in the repo's README.md would be easy to discover for the newcomers. I would also suggest a new section, such as Development, in the marketplace docs.

Could you also please add an example run of the new target in the PR description?

[github-actions]

Successfully created backport PR #523 for release-1.1.