[feature request] Add proxy param

[anisenBRU31]

Add proxy options on function pinoElasticSearch and pass it in new Client

  const client = new Client({
    node: opts.node,
    auth: opts.auth,
    cloud: opts.cloud,
    ssl: { rejectUnauthorized: opts.rejectUnauthorized },
    proxy: opts.proxy
  })

[mcollina]

Would you like to send a Pull Request to address this issue? Remember to add unit tests.