Extend resource configuration API to include resource metadata

[ulucinar]

Description of your changes

Fixes #6

This PR extends the existing upjet resource configuration API to allow configuration & overrides related to the resource metadata (probably scraped from Terraform registry). Some possible configuration scenarios covered as of now:

• Fixing syntax errors in the scraped examples from the Terraform registry, e.g., fix azurerm_key_vault_access_policy.example-user's key_permissions attribute.
• Replacing/injecting attributes, if desired, in the extracted example manifest (resource specific or provider-wide), e.g., injecting a region attribute for all/select resources in provider-aws
• Manipulating/replacing reference fields, e.g., replace location references in provider-azure
• Marking resources that require globally unique names, such as the Azure Key Vaults or AWS S3 buckets.

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

A resource specific metadata override example:

p.AddResourceConfigurator("azurerm_disk_encryption_set", func(r *config.Resource) {
                ...
		if err := r.MetaResource.Examples[0].SetPathValue("location", "the middle of nowhere"); err != nil {
			panic(err)
		}
	})

Or, as expected, a provider-wide metadata configuration can be performed as follows (in for example, config/provider.go):

        ...
	for _, r := range pc.Resources {
		if err := r.MetaResource.Examples[0].SetPathValue("region", "Test Region"); err != nil {
			panic(err)
		}
	}

An example manifest generated using these configuration overrides on top of scraped metadata:

apiVersion: compute.azure.upbound.io/v1beta1
kind: DiskEncryptionSet
metadata:
  name: example
spec:
  forProvider:
    identity:
    - type: SystemAssigned
    keyVaultKeyId: ${azurerm_key_vault_key.example.id}
    location: the middle of nowhere
    region: Test Region
    resourceGroupNameRef:
      name: example
  providerConfigRef:
    name: default

To configure a unique name to be generated by the test runner, one may use:

p.AddResourceConfigurator("azurerm_key_vault", func(r *config.Resource) {
    ...
    r.MetaResource.ExternalName = meta.RandRFC1123Subdomain

The generated example manifest now contains:

apiVersion: keyvault.azure.upbound.io/v1beta1
kind: Vault
metadata:
  annotations:
    crossplane.io/external-name: '{{ .Rand.RFC1123Subdomain }}'
...

which is to be substituted by the test runner at runtime with a random RFC1123 subdomain string.

[muvaf]

If we're planning on keeping this as single file, would it make sense to use go:embed similar to schema so we don't need to worry about reading files in Upjet?

[muvaf]

Looks like that if we use go:embed, we don't need to add RootDir and ProviderMetadataPath fields to config.Provider, which is preferable.

[ulucinar]

I think at some point it's better to split the monolithic provider-metadata.yaml file. My proposal would be to do the per-resource splitting in further rounds, but we may also do so as part of the ongoing https://github.com/upbound/official-providers/issues/19 issue.

[muvaf]

Honestly, I can be convinced either way regarding single or multiple files. But if we do end up going with a single file, I'd prefer to go:embed it so that we do not deal with file reading at all in Upjet.

[ulucinar]

Done. We now go:embed the monolithic provider metadata file. We may later split the provider metadata per resource in the future as discussed.

[ulucinar]

Thanks @muvaf for the comments!

[muvaf]

Thank you @ulucinar ! It's all coming together!!

[muvaf]

Since we're using this only in NewProvider, would it make sense to not expose it in Provider struct?

[ulucinar]

Done.

[muvaf]

nit: we can omit providerConfigRef altogether since it defaults to default.

[ulucinar]

Done.

[muvaf]

Since we're converting to []byte anyway, we might consider accepting providerMetadata as []byte in NewProvider. go:embed supports it.

[ulucinar]

Done.