brillo manifest: Add conscript project

This is needed by signapk.
diff --git a/default.xml b/default.xml
index 0465032..1e0beb4 100644
--- a/default.xml
+++ b/default.xml
@@ -53,6 +53,7 @@
   <project path="external/c-ares" name="platform/external/c-ares" groups="bdk" />
   <project path="external/clang" name="platform/external/clang" groups="bdk" />
   <project path="external/compiler-rt" name="platform/external/compiler-rt" groups="bdk" />
+  <project path="external/conscrypt" name="platform/external/conscrypt" groups="bdk" />
   <project path="external/cros/system_api" name="platform/external/cros/system_api" groups="bdk" />
   <project path="external/curl" name="platform/external/curl" groups="bdk" />
   <project path="external/dbus" name="platform/external/dbus" groups="bdk" />