enable sending voice message through messageSendFile()

[MachengShen]

Support sending amr/mp3 files through messageSendFile(), will check the mimetype of the Filebox file, and correspondingly adjust the request header sent to wechat OA server.

Test plan:

let fileBox_audio = FileBox.fromFile('xxx.mp3')
if (msgPayload.fromId){
  await puppet.messageSendFile(msgPayload.fromId!, fileBox_audio)
}  

Anticipated result: user should receive a voice message (recorded in 'xxx.mp3') from the wechat OA.

Link to #19

[CLAassistant]

All committers have signed the CLA.

[huan]

Thank you very much for adding audio support to our Puppt Official Account!

Please follow my reviews and make the CI green, then it will be ready to be merged.

And please link to the related issue in the PR so we can group all related information together.

Link to: #19

[huan]

Please keep this log verbose output, because we always log a function when it's being called.

[MachengShen]

ok, i uncommented it. just to note that this line does not work for audio file such as .mp3, and will throw an error.

[huan]

Can we make this logic more robust?

I'd like to suggest that:

1. we do a switch for checking file.mimeType and set the MsgType correctly
2. we throw an exception for the unknown mimeType instead of failing silently

[MachengShen]

thanks for the suggestions, have updated

[huan]

LGTM

[huan]

Thank you very much for your contribution!

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[huan]

This PR has been published on wechaty-puppet-office-account@0.5.42