feat(sql/catalog): Support ALTER TABLE IF EXISTS (#2542)

* feat(sql/catalog): ALTER TABLE IF EXISTS
* Remove debug statements
* Remove print statement

Author: kyleconroy

internal/endtoend/testdata/ddl_alter_table_if_exists/postgresql/pgx/v4/go/db.go

@@ -0,0 +1,2 @@
+-- name: Placeholder :exec
+SELECT 1;

internal/endtoend/testdata/ddl_alter_table_if_exists/postgresql/pgx/v4/go/models.go

@@ -0,0 +1,7 @@
+ALTER TABLE IF EXISTS foo ADD COLUMN bar integer;
+ALTER TABLE IF EXISTS bar RENAME COLUMN bar TO baz;
+ALTER TABLE IF EXISTS bat RENAME CONSTRAINT bar TO baz;
+ALTER TABLE IF EXISTS baz RENAME TO bar;
+ALTER TABLE IF EXISTS goo SET SCHEMA bar;
+ALTER TABLE IF EXISTS gob ATTACH PARTITION partition_name DEFAULT;
+ALTER TABLE IF EXISTS doo DETACH PARTITION partition_name;

internal/endtoend/testdata/ddl_alter_table_if_exists/postgresql/pgx/v4/go/query.sql.go

@@ -0,0 +1,13 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "engine": "postgresql",
+      "sql_package": "pgx/v4",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}

internal/endtoend/testdata/ddl_alter_table_if_exists/postgresql/pgx/v4/query.sql

@@ -0,0 +1,2 @@
+-- name: Placeholder :exec
+SELECT 1;