Log repo.* config variables in git trace2 logger.

Bug: [google internal] b/181758736
Testing:
- Unit tests
- Verified repo git trace2 logs had expected data

Change-Id: I9af8a574377bd91115f085808c1271e9dee16a36
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/299182
Tested-by: Ian Kasprzak <iankaz@google.com>
Reviewed-by: Mike Frysinger <vapier@google.com>
Reviewed-by: Raman Tenneti <rtenneti@google.com>

git_config.py

@@ -145,6 +145,21 @@ class GitConfig(object):
     except ValueError:
       return None
 
+  def DumpConfigDict(self):
+    """Returns the current configuration dict.
+
+    Configuration data is information only (e.g. logging) and
+    should not be considered a stable data-source.
+
+    Returns:
+      dict of {<key>, <value>} for git configuration cache.
+      <value> are strings converted by GetString.
+    """
+    config_dict = {}
+    for key in self._cache:
+      config_dict[key] = self.GetString(key)
+    return config_dict
+
   def GetBoolean(self, name):
     """Returns a boolean from the configuration file.
        None : The value was not defined, or is not a boolean.