option to include yaml tags

[deitch]

A first attempt at resolving https://github.com/oapi-codegen/oapi-codegen/issues/1696

As request in that issue, I made it with yaml disabled by default, but could be enabled in output-options.

I explored making a CLI flag as well, but all of those that control config are listed as deprecated, and it says to use new config file style, so I left it as controllable via config file alone.

I probably missed something, in the tests and/or the templates. I did run it manually and it generated as expected, and I ran make test, so no regression should have been introduced. Looking for feedback on it.