Feature: add support for proxying http traffic (outbound)

[davehorton]

Several jambonz components need to reach out to the internet to connect to services, e.g.:

• webhook / websocket requests (from unidici)
• hosted tts
• hosted stt

In some environments, it may be necessary to send all such traffic from jambonz through a customer-provided outbound proxy such as squid, nginx or similar. We should add support for two new env vars:

• JAMBONES_HTTP_PROXY_IP
• JAMBONES_HTTP_PROXY_PORT

If provided, then webhooks and websocket requests (outbound) should go through the proxy at the configured address. The proxy must be a passthru proxy (i.e. using the CONNECT method) so that it does not look like a man in the middle attack.

Also, as a first pass, Microsoft Azure TTS and STT, which support a proxy setting, should be able to route the traffic through this proxy as well.

[davehorton]

@xquanluu please as a first thing work on making these env vars work for unidici so we can make webhook requests and send notifications through a global proxy, if configured.

See nodejs/undici#1650 for some discussion and details. It appears unidici does not directly support this out of the box, but it does support / expose a ProxyAgent class that can be used, and there is some sample code. Please test using squid.

[davehorton]

sample code: nodejs/undici#1650 (comment)