Multiple Knex configuration

[davidedantonio]

Hi everyone, I'm Davide! I have multiple database connection and I can't register the plugin for all these connection. I receive the message

FastifyError [FST_ERR_DEC_ALREADY_PRESENT]: The decorator 'knex' has already been added!

Is there any reason why this cannot be done? I think that with a simple update it's possible to manage multiple knex instance. For example:

...
    const name = opts.name || 'knex'
    if (opts.name) {
      delete opts.name
    }

    const handler = knex(opts);

    fastify
      .decorate(name, handler)
      .addHook('onClose', (instance, done) => {
        /* istanbul ignore else */
        if (instance.name === handler) {
          instance.name.destroy();
          delete instance.name;
        }

        done();
      });
...

Can I send a pull request with these updates? It would be great for me to help develop the plugin! Thanks