fixed transcription is not received when call is terminated

[xquanluu]

#1246
#997

[xquanluu]

Hi @davehorton @vdharashive @rammohan-y

My solution is for fixing transcription is not received when call is terminated by:
1/ in media-endpoint.js: which is a utils for creating new endpoint, feature server will have a common place to create Freeswitch endpoint, the endpoint is configured for all needed features.

The transcription issue are:
1/ feature server sends stopTranscription command too soon that we missed the transcription
2/ feature server destroys endpoint too soon that we missed the transcription

To fix above issue, If JAMBONES_TRANSCRIBE_EP_DESTROY_DELAY_MS is enabled, this PR does graceful shutdown for the endpoint by:
1/ override endpoint startTranscription: to let the endpoint know if the ep is in transcribe task
2/ override endpoint stopTranscription: if the endpoint is in transcribe task, the stopTranscription will be delayed until one of condition is matched: transcription is received or JAMBONES_TRANSCRIBE_EP_DESTROY_DELAY_MS timeout is passed.

3/ override endpoint destroy: if the endpoint is in transcribe task, the destroy will be delayed until one of condition is matched: transcription is received or JAMBONES_TRANSCRIBE_EP_DESTROY_DELAY_MS timeout is passed.

Please help me to review the PR and let me know if something need to be fixed

[rammohan-y]

@xquanluu we found two cases in which the stopTranscription should stop immediately even if the JAMBONES_TRANSCRIBE_EP_DESTROY_DELAY_MS is set, one is when stopTranscription is invoked during ASR fallback and stopTranscription invoked when the call transcription_status is paused

Can you address these scenarios

As the PR is big, it will take some time to test

[rammohan-y]

This PR fixes all the issues, delayed termination and delayed stopTranscription when JAMBONES_TRANSCRIBE_EP_DESTROY_DELAY_MS is specified.
There is no delay for pause transcription, ASR fallback and stopAmd

@xquanluu @vdharashive @davehorton