api: list: return 'formats' info in a better structured way

returning the formats in the way of:
```
"format": [
    {
        "format1" => 1,
        "format2" => 1,
        ...
    },
    "defaultFormat"
]
```

is not a very good return format, since it abuses an array as a
tuple, and unnecessarily encodes a list of formats as an object.
Also, we can't describe it properly in JSONSchema in perl, nor our
perl->rust generator is able to handle that.

Instead, return it like this:
```
"formats": {
    "default": "defaultFormat",
    "supported": ["format1", "format2", ...]
}
```

which makes it much more sensible for an api return schema, and it's
possible to annotate it in the JSONSchema.

For compatibility reasons, keep the old property around, and add a
comment to remove with 10.0

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>

src/PVE/API2/Storage/Status.pm

@@ -178,6 +178,7 @@ __PACKAGE__->register_method({
                     optional => 1,
                 },
 
+                # FIXME: remove with 10.0
                 # we can't include this return schema, since we cannot properly
                 # describe what it actually is with the json schema:
                 #
@@ -185,9 +186,31 @@ __PACKAGE__->register_method({
                 # object, and the second is a string.
                 #format => {
                 #    description => "Lists the supported and default format."
-                #        . " Only included if 'format' parameter is set.",
+                #        . "Deprecated (use 'formats' instead). Only included "
+                #        . "if 'format' parameter is set.",
                 #    optional => 1,
                 #},
+                formats => {
+                    description => "Lists the supported and default format. Use"
+                        . " 'formats' instead. Only included if 'format' parameter is set.",
+                    optional => 1,
+                    type => 'object',
+                    properties => {
+                        supported => {
+                            type => 'array',
+                            description => 'The list of supported formats',
+                            items => {
+                                type => 'string',
+                                enum => [qw(qcow2 raw subvol vmdk)],
+                            },
+                        },
+                        default => {
+                            description => "The default format of the storage.",
+                            type => 'string',
+                            enum => [qw(qcow2 raw subvol vmdk)],
+                        },
+                    },
+                },
             },
         },
         links => [{ rel => 'child', href => "{storage}" }],