/var/lib/rancher/k3s/server/manifests files must conform to RFC1123

[strowi]

Environmental Info:
K3s Version:
v1.24.10+k3s1

Describe the bug:
I put some manifests into /var/lib/rancher/server/manifests containing underscores hcloud_secret.yaml, and it didn't get deployed.
Since this is about the filename, which is totally valid (and common pattern) on most filesystems i wouldn't expect this to be a problem.
Looking into the k3s logs i found:

[12874]: time="2023-03-02T10:49:26Z" level=error msg="Failed to process config: failed to process /var/lib/rancher/k3s/server/manifests/hcloud_secret.yaml: Addon.k3s.cattle.io \"hcloud_secret\" is invalid: metadata.name: Invalid value: \"hcloud_secret\": a lowercase RFC 1123 subdomain must consist of lower case alphanumeric characters, '-' or '.', and must start and end with an alphanumeric character (e.g. 'example.com', regex used for validation is '[a-z0-9]([-a-z0-9]*[a-z0-9])?(\\.[a-z0-9]([-a-z0-9]*[a-z0-9])?)*')

If this is wanted/expected behaviour for k3s i would at least want a documentation update since this isn't mentioned on https://docs.k3s.io/advanced#auto-deploying-manifests and took me some time to figure out.

Steps To Reproduce:
Put a valid file containing an underscore into the above folder.

Expected behavior:

I would expect it to deploy.

Actual behavior:

It doesn't get deployed.

Additional context / logs:

[caroline-suse-rancher]

Fixed in the above PR