Annotate credentials with source backend label

With this, we can now communicate to users what credentials are legacy
and behave different from others.

Closes datalad#246

datalad_next/commands/credentials.py

@@ -384,6 +384,8 @@ def custom_result_renderer(res, **kwargs):
             '✓' if res.get('cred_secret') else '✗',
         )
 
+        if res.pop('from_backend', None) == 'legacy':
+            res['type'] = 'legacy-credential'
         if 'message' not in res:
             # give the names of all properties
             # but avoid duplicating the type, hide the prefix,

datalad_next/credman/manager.py

@@ -500,15 +500,17 @@ def query_(self, **kwargs):
         done = set()
         known_credentials = set((n, None) for n in self._get_known_credential_names())
         from itertools import chain
-        for name, type_hint in chain(
+        for name, legacy_type_hint in chain(
                 _yield_legacy_credential_names(),
                 known_credentials):
             if name in done:
                 continue
             done.add(name)
-            cred = self.get(name, _prompt=None, _type_hint=type_hint)
+            cred = self.get(name, _prompt=None, _type_hint=legacy_type_hint)
             if not cred:
                 continue
+            if legacy_type_hint is not None:
+                cred['_from_backend'] = 'legacy'
             if not kwargs:
                 yield (name, cred)
             else: