List{Branches,Tags}: Use "-S' as alias for "--start" instead of "-s"

Using upper case "-S" makes the API consistent with the other list
APIS:

- list changes
- list groups
- list projects

This will break any existing clients that use -s, but there are no
known clients doing that except the GWT UI (fixed in this change) and
the PolyGerrit UI (will be fixed in a follow-up change on master).

Change-Id: Ic9c73eb50c537957a14ab180cb5d5bbfa6c6f50d

gerrit-server/src/main/java/com/google/gerrit/server/project/ListTags.java

@@ -70,7 +70,7 @@ public class ListTags implements RestReadView<ProjectResource> {
 
   @Option(
     name = "--start",
-    aliases = {"-s"},
+    aliases = {"-S"},
     metaVar = "CNT",
     usage = "number of tags to skip"
   )