config api/plugins: let plugins define sensitive properties themselves

Hard-coding a list of sensitive properties means that custom plugins
cannot define their own sensitive properties for the on_add/on_update
hooks.

Have plugins declare the list of their sensitive properties in the
plugin data. For backwards compatibility, return the previously
hard-coded list if no such declaration is present.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Tested-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Reviewed-by: Wolfgang Bumiller <w.bumiller@proxmox.com>
Link: https://lore.proxmox.com/20250404133204.239783-6-f.ebner@proxmox.com

src/PVE/Storage/ZFSPlugin.pm

@@ -175,6 +175,7 @@ sub type {
 sub plugindata {
     return {
 	content => [ {images => 1}, { images => 1 }],
+	'sensitive-properties' => {},
     };
 }