feat(postgres): add native enum type support

[ErfanMomeniii]

Adds native PostgreSQL enum type support to PostgresAdapter.

Problem

PostgreSQL requires a two-step process for enum columns — first CREATE TYPE ... AS ENUM (...), then referencing that type in column definitions. Phinx only supported MySQL's inline ENUM('a','b') syntax.

See: #2258

Solution

Handle the full enum lifecycle automatically with the naming convention {table}_{column} (e.g. orders_status) to prevent cross-table collisions.

Operation	Behavior
createTable()	Emits CREATE TYPE before CREATE TABLE
addColumn()	Emits CREATE TYPE before ALTER TABLE
dropColumn()	Drops the associated enum type after column removal
dropTable()	Drops all associated enum types after table removal
getColumns()	Round-trips enums back as PHINX_TYPE_ENUM with values from pg_enum

Usage

$this->table('orders')
      ->addColumn('status', 'enum', [
          'values'  => ['pending', 'shipped', 'delivered'],
          'default' => 'pending',
      ])
      ->create();

Rollbacks work automatically — dropping a column or table cleans up the associated PostgreSQL type.

Tests

10 new integration tests covering create, add, drop column, drop table, round-trip, cross-table isolation, and schema-qualified tables.

Fixes #2258

[ErfanMomeniii]

Hi @dereuromark , could you please review it?

[dereuromark]

@MasterOdin took over maintainance.