Use Tesla as wrapper to supports multiple http client

[Matsa59]

Is your feature request related to a problem? Please describe.

We moved from HTTPoison to hackney using Tesla but pigeon use directly HTTPoison create a dep that we could easily avoid.

Describe the solution you'd like

Replace HTTPoison by Tesla to support more http client.

After reading the code base it sounds really easy to do. I can do it but I prefer to ask if this direction is ok for the community.
At the end, people could continue to use HTTPoison if they prefer to

[hpopp]

I agree that migrating to Tesla would be really nice, but there's a lot more to consider than the current HTTPoison usage in Pigeon. If we were to make such a change, I would want to deprecate Kadabra and update FCM and APNS to use Tesla as well. This introduces a lot of other considerations (eg, Tesla would have to use an HTTP/2-compliant adapter).

Let me think on it for a bit.