Create a label config for copying all scores if list of files is the same

This change allows creating new labels or setting to an old label a new
label config: copyAllScoresIfListOfFilesDidNotChange.

Labels that have this config set to true will copy all scores if the
list of files did not change. Renames count as the same file (= no file
change); as long as there are no explicit additions or deletions to the
list of files, the scores will be copied to the next patch-set.

Change-Id: I0051ea1236e6bd50a69455d799ce27081091d21a

proto/cache.proto

diff --git a/proto/cache.proto b/proto/cache.proto
index 8d575b7..f3db71f 100644
--- a/proto/cache.proto
+++ b/proto/cache.proto
@@ -443,6 +443,7 @@
   int32 max_positive = 16;
   bool can_override = 17;
   repeated string ref_patterns = 18;
+  bool copy_all_scores_if_list_of_files_did_not_change = 19;
 }
 
 // Serialized form of com.google.gerrit.server.project.ConfiguredMimeTypes.