BackingImage does not download URL correctly in some situation

[votdev]

Remove the Referer header that is automatically added by the http client. Without this header it is possible to download files that are redirected several times. This mimics the behaviour of curl and wget which do not submit the Referer header by default.

Which issue(s) this PR fixes:

longhorn/longhorn#7914

What this PR does / why we need it:

This PR removes the Referer header from the requests. This is necessary to allow downloads of files (e.g. ISO images) that are delivered from file hosters (e.g. SourceForge) via CDN which normally results in several redirects until the requested file is downloaded.

This PR mimics the default behaviour of tools like curl or wget.

[votdev]

Testplan

1. Create a file with the following content:

apiVersion: longhorn.io/v1beta2
kind: BackingImage
metadata:
  name: clonezilla
  namespace: longhorn-system
spec:
  sourceParameters:
    url: https://sourceforge.net/projects/clonezilla/files/clonezilla_live_alternative/20240116-mantic/clonezilla-live-20240116-mantic-amd64.iso
  sourceType: download

2. Apply it with k apply -f clonezilla.yaml.
3. Check the output:

$ k get backingimage -n longhorn-system
NAME                  UUID       SOURCETYPE   SIZE        AGE
clonezilla            42549254   download     102954      11s

This is the current state. The ISO is not downloaded properly.
4. Install the backing-image-manager image containing this PR.
5. Delete the clonezilla backing image via UI.
6. Apply it with k apply -f clonezilla.yaml.
7. Check the output:

$ k get backingimage -n longhorn-system
NAME                  UUID       SOURCETYPE   SIZE        AGE
clonezilla            9c339f0f   download     500170752   8s

8. Create another backing image.

apiVersion: longhorn.io/v1beta2
kind: BackingImage
metadata:
  name: systemrescue
  namespace: longhorn-system
spec:
  sourceParameters:
    url: https://fastly-cdn.system-rescue.org/releases/11.00/systemrescue-11.00-amd64.iso
  sourceType: download

9. Check the output:

$ k get backingimage -n longhorn-system
NAME                  UUID       SOURCETYPE   SIZE        AGE
systemrescue          28b76870   download     894435328   17s

[ChanYiLin]

LGTM, thanks for the contribution!

[innobead]

@mergify backport v1.6.x v1.5.x

[mergify]

backport v1.6.x v1.5.x

✅ Backports have been created

• #191 BackingImage does not download URL correctly in some situation (backport #182) has been created for branch v1.6.x
• #192 BackingImage does not download URL correctly in some situation (backport #182) has been created for branch v1.5.x