Replace call to included OpenAPI jar with a Maven process that can use a plugin (with wrapper?)

[jasonwjones]

Let's see if we can get away from having the OpenAPI JAR included in this repo, in favor of a small POM file that uses the plugin to accomplish the same thing, and can be called using the wrapper so it's easy for people that might not have Maven installed to simply run. Then, moving forward, it'll be a little easier to simply update the version of the generator without having to drop in a new binary, as we should hopefully be able to just update a version property in the POM and be done with it.

[billybooth]

Adding myself on this one as well. Ben can feel free to work the POM, but keep in mind, @jasonwjones that it's assuredly very atypical to use maven to bring in a tooling dependency for a .NET project.

[jasonwjones]

@billybooth Fair enough, although I presume the process to build from the OpenAPI doc will generally only be used by us and the usage of the JAR in the first place already necessitates having Java, so in this case I think it makes sense to use the plugin so that we can pull the binary out and make changes more transparent/conducive to version control.