init/sync: add --no-tags to match --tags

While this provides a way to undo earlier command line options (e.g.
`repo sync --tags --no-tags`) which can be helpful for scripting &
automation, this more importantly allows the user to override the
manifest settings for syncing tags from a project.

Bug: https://crbug.com/gerrit/12401
Change-Id: Id4c36cd82e6ca7cb073b5d63a09f6c7ccdebba83
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/304904
Reviewed-by: Raman Tenneti <rtenneti@google.com>
Tested-by: Mike Frysinger <vapier@google.com>

project.py

@@ -1044,7 +1044,7 @@ class Project(object):
                        current_branch_only=None,
                        force_sync=False,
                        clone_bundle=True,
-                       tags=True,
+                       tags=None,
                        archive=False,
                        optimized_fetch=False,
                        retry_fetches=0,
@@ -1125,8 +1125,8 @@ class Project(object):
       elif self.manifest.default.sync_c:
         current_branch_only = True
 
-    if not self.sync_tags:
-      tags = False
+    if tags is None:
+      tags = self.sync_tags
 
     if self.clone_depth:
       depth = self.clone_depth