Allow metamodel output/package customization

[nitroin]

First of all, thank you for this cool project!

Q: I'd would like to know if metamodels can be generated in a reserved package.

Now metamodels are generated "alongside" entity objects, ie:
src/main/java/com/speedment/jpastreamer/demo/quarkus/hibernate/panache/model/Film.java
Produce the metamodel in:
target/generated-sources/annotations/com/speedment/jpastreamer/demo/quarkus/hibernate/panache/model/Film$.java

Both having the package:

package com.speedment.jpastreamer.demo.quarkus.hibernate.panache.model;

This produce some IDE confusion both in Eclipse and VSCode (see this and that).

Manually moving metamodels under a different package, for example:

package com.speedment.jpastreamer.demo.quarkus.hibernate.panache.model.meta;

Resolve all the IDE tantrum.

[nitroin]

Duplicate of #280