tapd: add x_only_group_key to key_group_info_view

We want to be able to match the group key with universe roots, which use
the x-only (32-byte) part of the group key. To make the matching easier,
we add a x_only_group_key version of the tweaked group key to the
key_group_info_view.

tapdb/sqlc/migrations/000002_assets.up.sql

@@ -331,7 +331,8 @@ CREATE VIEW genesis_info_view AS
 CREATE VIEW key_group_info_view AS
     SELECT
         witness_id, gen_asset_id, witness_stack, tapscript_root,
-        tweaked_group_key, raw_key, key_index, key_family
+        tweaked_group_key, raw_key, key_index, key_family,
+        substr(tweaked_group_key, 2) AS x_only_group_key
     FROM asset_group_witnesses wit
     JOIN asset_groups groups
         ON wit.group_key_id = groups.group_id