Generate enum types from Postgres and MySQL

[JasonShin]

Context So far sqlx-ts wasn't able to generate enum types from DB - instead it has generated an any type. With this PR, sqlx-ts will be able to generate enum types, but it will generate all possible enum values as an union of strings

e.g.

export type UsersQueryParams = [];

export interface IUsersQueryResult {
    enum1: 'x-small' | 'small' | 'medium' | 'large' | 'x-large';
};

export interface IUsersQueryQuery {
    params: UsersQueryParams;
    result: IUsersQueryResult;
};