Add external/dokka to manifest.xml.

Bug: 74354142
Change-Id: Ia155e3558dae367ce38760812afbdb0fab710738

default.xml

@@ -127,6 +127,7 @@
   <project path="external/dng_sdk" name="platform/external/dng_sdk" groups="pdk" />
   <project path="external/dnsmasq" name="platform/external/dnsmasq" groups="pdk" />
   <project path="external/doclava" name="platform/external/doclava" groups="pdk" />
+  <project path="external/dokka" name="platform/external/dokka" groups="pdk" />
   <project path="external/drm_hwcomposer" name="platform/external/drm_hwcomposer" groups="drm_hwcomposer,pdk-fs" />
   <project path="external/droiddriver" name="platform/external/droiddriver" groups="pdk" />
   <project path="external/drrickorang" name="platform/external/drrickorang" groups="pdk" />