Make Schema output path configurable, and include referenced schema files

[kito99]

Currently the plugin automatically copies the schema file to a folder called graphql-apigen-schema in the target output path (classes) folder. Also, if the schema file references any other files, they are not included.

Ideally, the output path for the schema should be configurable, and it should include all referenced *.graphql files.

[brimworks]

Making the output path configurable, should be a simple change to ApiGenMojo.java, pull requests are welcomed :).

Regarding schema files that reference other files, I assume you mean referencing schema files from other maven modules? If so, the expectation is for the generated code to come from the maven module dependencies and therefore the dependent code is not regenerated.

[kito99]

With regards to references, I'm talking about files within the same folder. For example, we have several schema files:

/schema/Schema.graphql
/schema/types/Type1.graphql
/schema/types/Type2.grpahql
/schema/types/Type3.grpahql

All of these files are being converted properly, but only Schema.graphql is being copied to the output folder.