Allowing client-end API Key injection

[myselfhimself]

Hello,
so far the Deepgram proxy retrieves and uses a single Deepgram API Key from local configuration.
This suits "accountless" Deepgram SDK clients, but in some situations (eg. Deepgram-based plugins in multimedia editing software), the client side may want to allow a user to provide a custom API Key.

Hints on workarounds for this:

• setting extra= GET parameters of outgoing client requests to a string value like myCustomApiKey:<theDeepgramToken> ; the proxy reads it then discards the extra parameter before passing the request over to the Deepgram API host
• setting an extra HTTP header eg. (myCustomApiKey: <token>), which the proxy intercepts, reads, discards and passes on similarly.

If ever one of those approaches seems good to you, I can contribute a PR.
I think this could benefit many developers.

😉