Add support for moshi-kotlin-codegen

[cortinico]

We're currently generating code that relies on moshi-kotlin:

swagger-gradle-codegen/plugin/src/main/resources/kotlin/tools/GeneratedCodeConverters.kt.mustache

Lines 10 to 14 in ed70186

	private val moshi = Moshi.Builder()
	.add(XNullableAdapterFactory())
	.add(KotlinJsonAdapterFactory())
	.add(TypesAdapterFactory())
	.build()

This has the side effect of pulling in the kotlin-reflect dependency that is a pretty big jar.

We should consider moving over to moshi-kotlin-codegen.

Ideally we just need to generate the @JsonClass annotation for our data classes and make sure we provide proper proguard rules for it.

[filipemp]

[BLOCKED] moshi-kotlin-codegen generates code that doesn't compile for ReservedKeywords.kt
It looks like this

override fun toJson(writer: JsonWriter, value: ReservedKeywords?) {
        if (value == null) {
            throw NullPointerException("value was null! Wrap in .nullSafe() to write nullable values.")
        }
        writer.beginObject()
        writer.name("class")
        nullableStringAdapter.toJson(writer, value.class)
        writer.name("for")
        nullableStringAdapter.toJson(writer, value.for)
        writer.name("operator")
        nullableStringAdapter.toJson(writer, value.operator)
        writer.name("val")
        nullableStringAdapter.toJson(writer, value.val)
        writer.name("var")
        nullableStringAdapter.toJson(writer, value.var)
        writer.name("when")
        nullableStringAdapter.toJson(writer, value.when)
        writer.endObject()
}

It has been addressed already but not released

[cortinico]

Thanks for the investigation @filipemp
Let's keep it open for now and wait for moshi 1.9.
If you have a branch ready, please send it out as a Draft PR and we can already do a first-pass review