require url scheme for credential type url inputs

This adds a url formatting type for credential input string fields
The validator for this formatting type will throw an error if the
provided url string doesn't have a url schema.

awx/main/credential_plugins/azure_kv.py

@@ -10,6 +10,7 @@ azure_keyvault_inputs = {
         'id': 'url',
         'label': _('Vault URL (DNS Name)'),
         'type': 'string',
+        'format': 'url',
     }, {
         'id': 'client',
         'label': _('Client ID'),