fix: Detect default values for String types in OpenAPI output (#1928)

test/fixtures/schema.sql

@@ -1751,6 +1751,15 @@ CREATE TABLE test.openapi_types(
   "a_double_precision" double precision
 );
 
+CREATE TABLE test.openapi_defaults(
+  "text" text default 'default',
+  "boolean" boolean default false,
+  "integer" integer default 42,
+  "numeric" numeric default 42.2,
+  "date" date default '1900-01-01'::date,
+  "time" time default '13:00:00'::time without time zone
+);
+
 create function add_them(a integer, b integer)
 returns integer as $$
   select a + b;