Add tags to obs_getavailablegeometries

Fixes #260

* Adds `geom_type`, `geom_extra`, and `geom_tags` to `OBS_GetAvailableGeometries`. This brings it up to spec with existing docs.
* Adds `timespan_type`, `timespan_extra`, and `timespan_tags` to `OBS_GetAvailableTimespans` for consistency.

src/pg/test/expected/42_observatory_exploration_test.out

@@ -120,6 +120,9 @@ t
 _obs_getavailablegeometries_bg_not_1996
 t
 (1 row)
+_obs_getavailablegeometries_has_boundary_tag
+t
+(1 row)
 _obs_getavailabletimespans_2010_2014_in_all
 t
 (1 row)

src/pg/test/sql/42_observatory_exploration_test.sql

@@ -289,6 +289,11 @@ FROM cdb_observatory.OBS_GetAvailableGeometries(
 ) WHERE valid_timespan = True)
 AS _obs_getavailablegeometries_bg_not_1996;
 
+SELECT 'subsection/tags.boundary' IN (SELECT (Jsonb_Each(geom_tags)).key
+FROM cdb_observatory.OBS_GetAvailableGeometries(
+  ST_SetSRID(ST_MakePoint(-73.9, 40.7), 4326)
+)) AS _obs_getavailablegeometries_has_boundary_tag;
+
 --
 -- OBS_GetAvailableTimespans tests
 --