Open api generation

[juanpedromoreno]

What this does?

This PR resumes the work by @BeniVF , providing support for code generation from Open API specifications.

Checklist

• Reviewed the diff to look for typos, println and format errors.
• Updated the docs accordingly.

[juanpedromoreno]

There still some binary issues with circe, after the recent build upgrade (previously was working).

[info] [warn] There may be incompatibilities among your library dependencies; run 'evicted' to see detailed eviction warnings.
[info] [error] java.lang.NoSuchMethodError: sbt.package$.fileJsonFormatter()Lsjsonnew/JsonFormat;
[info] [error] 	at higherkindness.mu.rpc.idlgen.IdlGenPlugin$autoImport$.srcGenSourceDirs$lzycompute(IdlGenPlugin.scala:60)
[info] [error] 	at higherkindness.mu.rpc.idlgen.IdlGenPlugin$autoImport$.srcGenSourceDirs(IdlGenPlugin.scala:59)
[info] [error] 	at $1a2dcb12ba29963163ce$.root$lzycompute(build.sbt:19)
[info] [error] 	at $1a2dcb12ba29963163ce$.root(build.sbt:11)
[info] [error] 	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[info] [error] 	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[info] [error] 	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)

[juanpedromoreno]

Thanks @fedefernandez for the fix! Actually, I think we don't need to add the build.properties files as part of the scripted tests... as you pointed out, looks like a bug in sbt.

[juanpedromoreno]

... and @BeniVF, thank you for your hard work in this new feature!

[fedefernandez]

Looks good to me, left a minor comment

[juanpedromoreno]

@BeniVF thanks for the review. I think this is now ready for a second look. Thanks.