codec_opus: Add download ability to menuselect

Updated codecs/codecs.xml to add codec_opus to the external
download list.

ASTERISK-26409

Change-Id: Ia07b36539f30e852125fb2b94147dc9774df31a4
(cherry picked from commit 2cdab0e36eec4997ca3bd85aa09efc477038e31c)
(cherry picked from commit e9684f3acd0e8def0df582c1505dd39dd3fd1610)

codecs/codecs.xml

+<member name="codec_opus" displayname="Download the Opus codec from Digium.  See http://downloads.digium.com/pub/telephony/codec_opus/README.">
+	<support_level>external</support_level>
+	<depend>xmlstarlet</depend>
+	<depend>bash</depend>
+	<depend>res_format_attr_opus</depend>
+	<defaultenabled>no</defaultenabled>
+</member>
 <member name="codec_silk" displayname="Download the SILK codec from Digium.  See http://downloads.digium.com/pub/telephony/codec_silk/README.">
 	<support_level>external</support_level>
 	<depend>xmlstarlet</depend>