feat(opapi): allow getting state without exporting it

[franklevasseur]

This will allow doing:

import { OpenApi } from '@bpinternal/opapi'
import { api } from '@botpress/api'

const { errors } = api.getState()

const chatApi = OpenApi({
  metadata: {
    description: '...',
    server: 'http://localhost:3000',
    title: '...',
    version: '0.0.0',
  },
  errors // simply reuse errors from the Botpress API
})

instead of:

// gen.ts
import { api } from '@botpress/api'
api.exportState("./gen")

// index.ts
import { state } from './gen'
const chatApi = OpenApi({
  metadata: {
    description: '...',
    server: 'http://localhost:3000',
    title: '...',
    version: '0.0.0',
  },
  errors: state.errors
})