feat: add --location flag to specify datacenter region

Allow users to specify which Hetzner datacenter location to use for
the temporary server during image upload. Defaults to fsn1 for
backward compatibility.

Available locations: fsn1, nbg1, hel1, ash, hil, sin

README.md

@@ -73,7 +73,8 @@ export HCLOUD_TOKEN="<your token>"
 hcloud-upload-image upload \
   --image-url "https://example.com/disk-image-x86.raw.bz2" \
   --architecture x86 \
-  --compression bz2
+  --compression bz2 \
+  --location nbg1  # Optional: defaults to fsn1
 ```
 
 To learn more, you can use the embedded help output or check out the [CLI help pages in this repository](docs/reference/cli/hcloud-upload-image.md).:
@@ -123,6 +124,7 @@ func main() {
 		ImageURL:         imageURL,
 		ImageCompression: hcloudimages.CompressionBZ2,
 		Architecture:     hcloud.ArchitectureX86,
+		Location:         &hcloud.Location{Name: "nbg1"}, // Optional: defaults to fsn1
 	})
 	if err != nil {
 		panic(err)