hg: support new clonebundles_manifest write protocol command

A new wire protocol command was introduced with Mercurial 6.5 -
https://repo.mercurial-scm.org/hg/rev/4238e6b22fc4 .

When a client (after negotiation with the server) decided to use this new
command, Kallithea would fail safely and require write permissions.

Fixed by adding it to the list of known read-only commands.

kallithea/config/middleware/simplehg.py

@@ -70,6 +70,7 b' cmd_mapping = {'
     'changegroupsubset': 'pull',
     'changesetdata': 'pull',
     'clonebundles': 'pull',
+    'clonebundles_manifest': 'pull',
     'debugwireargs': 'pull',
     'filedata': 'pull',
     'getbundle': 'pull',