Support loading a config from a `openapi-codegen.config.mts` file

[forivall]

When i use the mts file extension to define my config as a module, rather than allowing it to be treated as commonjs, the loading doesnt work properly. With npx openapi-codegen -c openapi-codegen.config.mts, i see

Type Error: Cannot read properties of undefined (reading 'source')
    at GenerateCommand.getFromOptions (file:///Users/emily.klassen/code/tmp/oapi-codegen-example/node_modules/@openapi-codegen/cli/lib/cli.js:282:47)
    at Object.task (file:///Users/emily.klassen/code/tmp/oapi-codegen-example/node_modules/@openapi-codegen/cli/lib/cli.js:364:32)
    at xe (file:///Users/emily.klassen/code/tmp/oapi-codegen-example/node_modules/@clack/prompts/dist/index.mjs:79:394)
    at GenerateCommand.execute (file:///Users/emily.klassen/code/tmp/oapi-codegen-example/node_modules/@openapi-codegen/cli/lib/cli.js:359:11)
    at async GenerateCommand.validateAndExecute (file:///Users/emily.klassen/code/tmp/oapi-codegen-example/node_modules/clipanion/lib/advanced/Command.mjs:49:26)
    at async Cli.run (file:///Users/emily.klassen/code/tmp/oapi-codegen-example/node_modules/clipanion/lib/advanced/Cli.mjs:227:24)
    at async Cli.runExit (file:///Users/emily.klassen/code/tmp/oapi-codegen-example/node_modules/clipanion/lib/advanced/Cli.mjs:236:28)

To work around this, i need to change the config like

// openapi-codegen.config.mts
import { defineConfig } from "@openapi-codegen/cli";
import {
  generateSchemaTypes,
  generateReactQueryComponents,
} from "@openapi-codegen/typescript";

export const example = defineConfig({
  example: {
    // can be overridden from cli
    from: {
      source: "github",
      owner: "fabien0102",
      repository: "openapi-codegen",
      ref: "main",
      specPath: "examples/spec.yaml",
    },

    // can be overridden from cli
    outputDir: "src/queries",

    to: async (context) => {
      // You can transform the `context.openAPIDocument` here, can be useful to remove internal routes or fixing some known issues in the specs ;)

      // Generate all the schemas types (components & responses)
      const { schemasFiles } = await generateSchemaTypes(context, {
        /* config */
      });

      // Generate all react-query components
      await generateReactQueryComponents(context, {
        /* config*/
        schemasFiles,
      });
    },
  },
}).example;

The primary motivation for using an mts file is, if i have a tsconfig which uses module: 'node16', the types will not resolve properly, as "@openapi-codegen/cli" et al are esm. Otherwise, i'd have to create another tsconfig specifically to target the config, which is less than ideal.