ClickHouse: `ALTER TABLE ... ADD COLUMN ... FIRST | AFTER col` fails to parse

[s5dsn-eqee]

ALTER TABLE t ADD COLUMN c UInt8 AFTER a
-- sql parser error: Expected: end of statement, found: AFTER

ClickHouse supports this, and the parser already handles it for MySQL. parse_column_position is hardcoded to dialect_of!(MySqlDialect | GenericDialect), and this should become a Dialect trait method so ClickHouse can enable it.