Issue Description

Is your feature request related to a problem? Please describe.

I have a OneToMany relationship between a Post and Comments. I noticed that this relationship provides me with the following methods:

     *    // getRoles...
     *    // setRoles...
     *    // addRoles...
     *    // addRole...
     *    // createRole...
     *    // removeRole...
     *    // removeRoles...
     *    // hasRole...
     *    // hasRoles...
     *    // countRoles...

In a particular use case that I have, I also need a createRoles method, which is not provided.

Describe the solution you'd like

I'd like the hasMany relationship to generate this method for me along with the other ones.

Why should this be in Sequelize

I think this is a valid use case. Just as we are able to addRoles and removeRoles, it makes sense to me that we should be able to createRoles too.

Issue Template Checklist

Is this issue dialect-specific?

• No. This issue is relevant to Sequelize as a whole.
• Yes. This issue only applies to the following dialect(s): XXX, YYY, ZZZ

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I don't know how to start, I would need guidance.
• No, I don't have the time, although I believe I could do it if I had the time...
• No, I don't have the time and I wouldn't even know how to start.