<!--- Verify first that your feature was not already discussed on GitHub -->
<!--- Complete *all* sections as described, this form is processed automatically -->

##### SUMMARY
<!--- Describe the new feature/improvement briefly below -->
azure_rm_galleryimageversion_module should be able to take data disk snapshots as input.

##### ISSUE TYPE
- Feature Idea

##### COMPONENT NAME
<!--- Write the short name of the module, plugin, task or feature below, use your best guess if unsure -->
azure_rm_galleryimageversion_module

##### ADDITIONAL INFORMATION
<!--- Describe how the feature would be used, why it is needed and what it would solve -->
Starting from SIG api version 2019-07-01, we support creating image version from snapshots, which contains 1 os disk snapshot and 0 to many data disk snapshots. By having this feature, it give customers full power to create image version from snapshots.

Here is a sample request entity:
{"name":"1.0.0","location":"West US","properties":{"publishingProfile":{"excludeFromLatest":false},"storageProfile":{"osDiskImage":{"source":{"id":"/subscriptions/<subId>/resourceGroups/rgName/providers/Microsoft.Compute/snapshots/osSnapshotName"}},"dataDiskImages":[{"lun":0,"source":{"id":"/subscriptions/<subId>/resourceGroups/rg/providers/Microsoft.Compute/snapshots/datadiskSnapshot1"}}]}}}

So for data disk, user needs to provide "lun" and "source".

<!--- Paste example playbooks or commands between quotes below -->
```yaml

```

<!--- HINT: You can also paste gist.github.com links for larger files -->

('/*' if o['type'] == 'list' else ''))
            if comparison != 'default' or not updatable:
                result[p] = {'updatable': updatable, 'comparison': comparison}
            if o.get('options'):
                self.create_compare_modifiers(o.get('options'), p, result)
    def default_compare(self, modifiers, new, old, path, result):
        '''
            Default dictionary comparison.
            This function will work well with most of the Azure resources.
            It correctly handles "location" comparison.
            Value handling:
                - if "new" value is None, it will be taken from "old" dictionary if "incremental_update"
                  is enabled.
            List handling:
                - if list contains "name" field it will be sorted by "name" before comparison is done.
                - if module has "incremental_update" set, items missing in the new list will be copied
                  from the old list
            Warnings:
                If field is marked as non-updatable, appropriate warning will be printed out and
                "new" structure will be updated to old value.
            :modifiers: Optional dictionary of modifiers, where key is the path and value is dict of modifiers
            :param new: New version
            :param old: Old version
            Returns True if no difference between structures has been detected.
            Returns False if difference was detected.
        '''
        if new is None:
            return True
        elif isinstance(new, dict):
            comparison_result = True