[rust-client] Ability to specify path of output

[lahabana]

Currently output is always generated as src/{apis,models} as done by:

openapi-generator/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/RustClientCodegen.java

Lines 85 to 86 in 1655275

	protected String apiFolder = "src/apis";
	protected String modelFolder = "src/models";

In our case we run with a very limited generator (we only want the models).

.openapi-generator-ignore:

**
.openapi-generator/*
!src/models/*.rs

What we end up doing is a little odd:

mkdir -p generated/rust
rm -rf ./src/api/models
docker run --user $(id -u) --rm -v "${PWD}:/local" -w /local/generated/rust openapitools/openapi-generator-cli:v7.12.0 generate -i /local/api/kiburi.v0.yml -g rust --config /local/.openapi-generator/rust/config.yaml
mv ./generated/rust/src/models ./src/api/model

Ideally it would be nicer if we could directly write the models etc to a subfolder inside our rust crate and not require manual modification.

I can imagine an additionalProperty: asModule: true or something like this.