[http client]: add HTTPS support

[niklasad1]

Attempt to add support for HTTPS via feature flags for rustls 0.21 for tokio 0.2 and rustls 0.22 tokio 1.0.
It's so damn ugly so I'm almost willing to maintain two different branches instead...

[dvdplm]

LGTM modulo nits.

It's surprising how hard the "easy" things are sometimes. I don't know how you could have done any better, but it sure is ugly.

[dvdplm]

I don't mind this actually, but some would make a big stink about having tests depend on the network.
@maciejhirsz do you have a strong opinion here (if not, then let's keep it as-is)?

[niklasad1]

well, I don't know how to test it locally, I suppose I need to create a self-signed certificate on localhost? This was simpler :)

Any suggestions?

[niklasad1]

I don't know how you could have done any better, but it sure is ugly.

We could enable TLS globally and make it non-optional, we have it for the websocket client now but I think optional is better even if it's harder to maintain and makes the code a little bit ugglier.

[dvdplm]

@niklasad1 is this ready to be merged?

[niklasad1]

@niklasad1 is this ready to be merged?

Yeah but I think we should provide a uniform TLS configuration for the clients i.e, either enable TLS for both or make it configurable. I filed #241 but should be addressed in another PR.

Also, #227 could make this cleaner I suppose ^^

[dvdplm]

Up to you to merge or not. FWIW I think TLS enabled for both is ok, at least for now.

[niklasad1]

I will enable TLS for both it makes configuration simpler for now.

After we remove the tokio features it would be easier for users to configure it.