Update ImmediateAcceptAdapter sample to notify users every 5 seconds when API call is pending

[ram-xv]

[PROBLEM DESCRIPTION] We have found that customer has long-running external API calls taking >15 secs and asking for feature request in regards to proactive messaging and custom actions for a Composer bot.

Feature request:

If an API request takes too long, the customer wants to proactively send a message (ex: every 5 seconds) to notify the user with a "loading" message to indicate the API call is in process.

This sample ImmediateAcceptAdapter already addresses the long-running request causing bot time-outs and responds to users like Already sleeping. Please wait... when API call is pending, only if we send a message.

The customer inquiry is to update the sample code such that it notifies the users every 5 secs or so when API call is pending.