S3 file asset repository URL validation

[elliotdobson]

/kind bug

1. What kops version are you running? The command kops version, will display
this information.
Client version: 1.29.2 (git-v1.29.2)

2. What Kubernetes version are you running? kubectl version will print the
version if a cluster is running or provide the Kubernetes version specified as
a kops flag.
Server Version: v1.29.7

3. What cloud provider are you using?
AWS

4. What commands did you run? What is the simplest way to reproduce this issue?
We are configuring local file asset repository however we are running into an issue when trying to update the cluster.

We tried to work around #16759 by specifying fileRepository as an S3 URL (even though the docs suggest this should not work) and to my surprise kOps accepted it and allowed us to apply it to the cluster.

However upon rolling the first control-plane node it did not come online and the update failed (some what expected).

1. Enable fileRepository in the Cluster spec (using an S3 URL as shown below)
2. Copy the file assets kops get assets --copy
3. Update the cluster kops update cluster
4. Roll an instance group kops rolling-update cluster

5. What happened after the commands executed?
New node fails to join the cluster and cluster validation fails.

Upon SSH'ing into the new node and checking the logs via journalctl -u cloud-final.service we see:

Aug 18 23:09:04 i-09ec9f0eec1f3fd13 cloud-init[1272]: == nodeup node config starting ==
Aug 18 23:09:04 i-09ec9f0eec1f3fd13 cloud-init[1272]: == Downloading nodeup with hash 73c2808ac814787ccca9671678d2919fc9023322c3b834ea47b3cef01d6841cb from s3://example-k8s-assets/kops/binaries/kops/1.29.2/linux/amd64/nodeup ==
Aug 18 23:09:04 i-09ec9f0eec1f3fd13 cloud-init[1272]: == Downloading s3://example-k8s-assets/kops/binaries/kops/1.29.2/linux/amd64/nodeup using curl -f --compressed -Lo nodeup --connect-timeout 20 --retry 6 --retry-delay 10 ==
Aug 18 23:09:04 i-09ec9f0eec1f3fd13 cloud-init[1272]: curl: (1) Protocol "s3" not supported or disabled in libcurl
Aug 18 23:09:04 i-09ec9f0eec1f3fd13 cloud-init[1272]: == Failed to download s3://example-k8s-assets/kops/binaries/kops/1.29.2/linux/amd64/nodeup using curl -f --compressed -Lo nodeup --connect-timeout 20 --retry 6 --retry-delay 10 ==

6. What did you expect to happen?
I expected the validation of a S3 URL in fileRepository to fail before we could apply the changes to the cluster, and have new nodes failing to start.

7. Please provide your cluster manifest. Execute
kops get --name my.example.com -o yaml to display your cluster manifest.
You may want to remove your cluster name and other sensitive information.

apiVersion: kops.k8s.io/v1alpha2
kind: Cluster
spec:
...
  assets:
    fileRepository: s3://example-k8s-assets/kops
...

8. Please run the commands with most verbose logging by adding the -v 10 flag.
Paste the logs into this report, or in a gist and provide the gist link here.

9. Anything else do we need to know?

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