refactor(sql/catalog): Improve Readability (#1595)

* Refactor catalog to self document

* Add comments and tests to pkg catalog

* Remove all unit test in favor of endtoend tests

* Refactor catalog getTable to improve readability

* Add endtoend test data for add table column

* Add endtoend test for mysql alter column type

* Add endtoend testdata for postgresql rename column

Author: jakoguta

internal/endtoend/testdata/ddl_alter_table_add_column/mysql/go/db.go

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

internal/endtoend/testdata/ddl_alter_table_add_column/mysql/go/models.go

@@ -0,0 +1,3 @@
+CREATE TABLE foo (bar text NOT NULL);
+ALTER TABLE foo ADD COLUMN baz integer;
+ALTER TABLE foo ADD bio integer;

internal/endtoend/testdata/ddl_alter_table_add_column/mysql/go/query.sql.go

@@ -0,0 +1,12 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "engine": "mysql",
+      "name": "querytest",
+      "schema": "schema.sql",
+      "queries": "query.sql"
+    }
+  ]
+}

internal/endtoend/testdata/ddl_alter_table_add_column/mysql/query.sql

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