proposal: IVR API, or PhoneCall API

[seeflood]

What would you like to be added

IVR API, or PhoneCall API

Developers can invoke this API to send voice messages to specific people.

Why is this needed

In the monitoring scenarios, monitor systems need to send alarm messages to people on-call.
The messages might be in different forms, including IM,SMS, Email and phone calls, depending on the level of urgency.

Product research

IVR product	Docs
Aliyun VMS	https://www.aliyun.com/product/vms
AWS Pinpoint	https://aws.amazon.com/cn/pinpoint/

Detailed Design

We need to consider the following factors:

• Portability
  For example, a monitor system might be deployed on alibaba cloud(using VMS to send voice message) or AWS (using AWS Pinpoint to send voice message). So portability is important here.

service IvrService {

  //Send voice using the specific template
  rpc SendVoiceWithTemplate(SendVoiceWithTemplateRequest) returns (SendVoiceWithTemplateResponse) {}

}

message SendVoiceWithTemplateRequest{
  // Required
  Template template = 1;
  // Required
  string to_mobile = 2;
  // This field is required by some cloud providers.
  string from_mobile = 3;
}

message Template{
  // Required
  string template_id = 1;
  // Required
  map<string, string>  template_params = 2;
}

message SendVoiceWithTemplateResponse{
  string message_id = 1;
}

[seeflood]

I submitted a PR #727
@kevinten10 @wenxuwan FYI

[github-actions]

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