Remove most HTML/CSS/JS assets from the backend service WAR

It only needs the error page HTML files; everything else isn't used by endpoints
served by the backend service and only serves to increase build times
(especially compiling all that JS).

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=202229514

java/google/registry/ui/BUILD

@@ -17,6 +17,13 @@ filegroup(
     ],
 )
 
+filegroup(
+    name = "minimal_runfiles",
+    srcs = [
+        "//java/google/registry/ui/html:html_files",
+    ],
+)
+
 filegroup(
     name = "runfiles_debug",
     srcs = [
@@ -41,6 +48,15 @@ zip_file(
     },
 )
 
+zip_file(
+    name = "minimal_war",
+    srcs = [":minimal_runfiles"],
+    out = "minimal_ui.war",
+    mappings = {
+        "domain_registry/java/google/registry/ui/html": "",
+    },
+)
+
 zip_file(
     name = "war_debug",
     srcs = [":runfiles_debug"],