Add a flag to enable Rikers

[ Merge of http://go/wvgerrit/191113 ]

Rikers will replace haystack for L3 protection. Haystack will still
be present to support offline licenses that were downloaded using
haystack in prior releases.

Bug: 262635528
Test: WVTS and unit tests
Change-Id: Idffa0002b2c7694df595fa9cac694806673377b8

libwvdrmengine/aconfig/wv_media_drm_flags.aconfig

@@ -6,3 +6,10 @@ flag {
   description: "Update CDM version to 18.0.2"
   bug: "311951236"
 }
+
+flag {
+  name: "enable_rikers"
+  namespace: "media_drm"
+  description: "Update CDM L3 protection to use Rikers"
+  bug: "262635528"
+}