v6: Improve support for ESM & CJS config files

We currently search for config/config.json and config/config.js

We should also automatically look for extensions .cjs, and .mjs so specifying the config file location is not necessary.

---

We should do the same for .sequelizerc (https://github.com/sequelize/cli/blob/main/src/core/yargs.js#L7): load it using importHelper and support files: .sequelizerc (as js), .sequelizerc.js, .sequelizerc.cjs, .sequelizerc.mjs, .sequelizerc.json.

[ephys]

Similarly to https://github.com/sequelize/cli/issues/960, we could detect the module type in package.json, and provide a --module cjs|esm option, and generate the right contents accordingly

[mariusa]

This PR https://github.com/sequelize/cli/pull/987 includes docs update which says ESM configuration files are supported for Node versions that support ESM natively, either via passing `--config config/config.mjs`, or by setting the `type` to `module` in your `package.json`.

In a project using "type": "module",, newly generated migration files are still non ESM:

npx sequelize-cli migration:create --name test1

generates

'use strict'

module.exports = {
    async up(queryInterface, Sequelize) {
        /**
         * Add altering commands here.
         *
         * Example:
         * await queryInterface.createTable('users', { id: Sequelize.INTEGER });
         */
    },

    async down(queryInterface, Sequelize) {
        /**
         * Add reverting commands here.
         *
         * Example:
         * await queryInterface.dropTable('users');
         */
    }
}