Fix external-name annotation configuration for examples

[ulucinar]

Description of your changes

Currently, we do not utilize the MetaResource.ExternalName configuration while generating example manifests. This PR fixes this.

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

Tested successfully with AWS's S3 bucket:

apiVersion: s3.aws.upbound.io/v1beta1
kind: Bucket
metadata:
  annotations:
    crossplane.io/external-name: ${Rand.RFC1123Subdomain}
  labels:
    testing.upbound.io/example-name: b
  name: b
spec:
  forProvider:
    region: us-west-1
    tags:
      Environment: Dev
      Name: My bucket

[sergenyalcin]

LGTM! Thanks @ulucinar