Add ST_AsEWKT binding

Closes #11836571

site_cubicweb.py

@@ -188,6 +188,13 @@ class ST_ASGEOJSON(FunctionDescr):
     rtype = 'String'
 
 
+class ST_AsEWKT(FunctionDescr):
+    minargs = 1
+    maxargs = 1
+    supported_backends = ('postgres',)
+    rtype = 'String'
+
+
 class ST_ASTEXT(FunctionDescr):
     minargs = 1
     maxargs = 2
@@ -344,3 +351,4 @@ register_function(ST_Y)
 register_function(ST_Z)
 register_function(ST_M)
 register_function(ST_EXTENT)
+register_function(ST_AsEWKT)