feat: use commander for cli args for better ux

[mnahkies]

replaces convict with commander for better argument validation,
and automatically generated -h / --help output.

Examples:

$ ./packages/openapi-code-generator/dist/index.js     
error: required option '-i --input <value>' not specified

$ ./packages/openapi-code-generator/dist/index.js --help
Usage: index [options]

Options:
  -i --input <value>           openapi3 schema file to generate from (env: OPENAPI_INPUT)
  -o --output <value>          directory to output generated code (env: OPENAPI_OUTPUT)
  -t --template <value>        template to use (choices: "typescript-koa", "typescript-fetch", "typescript-angular", env: OPENAPI_TEMPLATE)
  -s --schema-builder <value>  runtime schema parsing library to use (choices: "zod", "joi", default: "zod", env: OPENAPI_SCHEMA_BUILDER)
  -h, --help                   display help for command