e2e test date separators using the time enabled message endpoint

[petyosi]

We can populate messages across several days using this:

const jwt = JWTServerToken(STREAM_SECRET)
axios.post(`https://chat.stream-io-api.com/channels/messaging/group-9527/import?api_key=${STREAM_API_KEY}`, {
  messages: [{
    text: 'Hello in the past 888',
    user_id: 'some-user-id',
    created_at: '2021-02-11T20:51:25.030Z',
  }],
}, {
  headers: {
    'Stream-Auth-Type': 'jwt',
    Authorization: jwt,
  },
})