[REQ] Pair of server and storage codegens

Created by: ybelenko

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

I would like to generate both server stubs and MySQL schema for my project, but it's complicated to connect them right now. For instance, php-slim4 codegen doesn't know database table/field names whilemysql-schema generator cannot access model property names. With current implementation it's very hard to use ORM(Object-Relational Mapping) engines with Active Record patterns.

Describe the solution you'd like

I was the first person who said that standalone MySQL generator without server framework makes no sense. However @wing328 convinced me to create it anyway and I did. As a result, we have server and storage codegens which cannot communicate with each other. I'm not saying mysql-schema is completely useless right now, but it close to it.

1. The first thing that comes to mind is to create new mixed generator like php-slim4-mysql-schema, but it feels like a bad move.

2. Add option storage=mysql to current php-slim4 codegen sounds right, but I think it's very hard to implement, because then I need to merge all MySQL generator features completely into server codegen. Also it requires to wrap all MySQL codegen variables with new variable like {{#mysql-schema-codegen}}{{/mysql-schema-codegen}}. Maybe I'm overreacting and it's not so difficult.

Describe alternatives you've considered

I'm submitting this with discussion label because I would like to hear any suggestions from community.

cc @OpenAPITools/generator-core-team