[MySQL Handler] Support upsert mutation

[ryoheinagao]

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

I want to use GraphQL Mesh and MySQL like Hasura + PostgreSQL. When I want to upsert row data, I have to exec multiple mutation or combine select query.

Describe the solution you'd like

In GraphQL Mesh, you use mysql-utilities which has sdk for upsert SQL. So I suggest how about support upsert like other mutations and queries.

Describe alternatives you've considered

Alternative method is multiple calls from client-side or implement self made handlers.

[ardatan]

Would you create a PR for this change?

[ryoheinagao]

Thank you for your comment, I will try it.

[ryoheinagao]

Hi, I found a bug in mysql-utilities, so I will create a PR after tshemsedinov/node-mysql-utilities#64 merged.