feat(pgsql): ✨ Add templates for constraints and sequences

* Introduce new templates for creating unique, check, and foreign key constraints with existence checks.
* Add templates for setting sequence values and creating sequences.
* Refactor existing SQL generation logic to utilize new templates for better maintainability and readability.
* Ensure identifiers are properly quoted to handle special characters and reserved keywords.

pkg/writers/pgsql/templates/set_sequence_value.tmpl

@@ -0,0 +1,19 @@
+DO $$
+DECLARE
+  m_cnt bigint;
+BEGIN
+  IF EXISTS (
+    SELECT 1 FROM pg_class c
+    INNER JOIN pg_namespace n ON n.oid = c.relnamespace
+    WHERE c.relname = '{{.SequenceName}}'
+      AND n.nspname = '{{.SchemaName}}'
+      AND c.relkind = 'S'
+  ) THEN
+    SELECT COALESCE(MAX({{quote_ident .ColumnName}}), 0) + 1
+    FROM {{quote_ident .SchemaName}}.{{quote_ident .TableName}}
+    INTO m_cnt;
+    
+    PERFORM setval('{{quote_ident .SchemaName}}.{{quote_ident .SequenceName}}'::regclass, m_cnt);
+  END IF;
+END;
+$$;