docs: Add a note on external-name annotation on bucket

[terrytangyuan]

I stumbled upon this issue and it took my a while to figure out how the resolve the permission issue as the error is not very informative and actually misleading. Adding this note would help new users who might struggle with this as well.

I was having trouble creating a bucket that requires storage.buckets.get access to the Google Cloud Storage bucket while my SA has roles/storage.admin already (see below for more info).

managed/bucket.storage.gcp.crossplane.io cannot get GCP bucket attributes: googleapi: Error 403: [email protected] does not have storage.buckets.get access to the Google Cloud Storage bucket., forbidden

gcloud projects add-iam-policy-binding --role=roles/storage.admin a-test --member "serviceAccount:[email protected]"

Signed-off-by: Yuan Tang [email protected]

Description of your changes

Fixes #

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

[Feggah]

Sorry for my last comment, I think I've misread your issue. It wasn't about what the annotations does, it was actually about the uniqueness of the resource name, right? Then I agree with you 👍🏼 LGTM!

[turkenh]

Thank you @terrytangyuan!