fix(oapi-codegen): command line parsing compatibility

[stevenh]

Improve command line compatibility between old and new style configs so existing user setups work as expected where possible.

This restores -generate and -templates flags from deprecated states as the new configuration format doesn't provide the needed functionality with out them. It makes all but -alias-types work with new config files.

The -alias-types doesn't do anything in either config mode any more.

For -generate the use case is one configuration and multiple output files for different generation types, which we use extensively.

For -templates having to have go .tmpl inside a .yaml config file works for simple snippets but for large templates its not practical, hence the direction option is required.