allow per request TLS settings

[weissi]

Currently, we configure TLS globally per HTTPClient. Usually, that's fine but there are use cases where we need different TLS settings per server etc.

As @Lukasa point out, this unfortunately has consequences for the connection pool: Currently we key the pool with (protocol, host, port) which would then no longer work and we'd have to change the key to (protocol, host, port, TLS config) which doesn't sound too bad of a change and enables quite a few new use cases.

[weissi]

API could be

HTTPClient.Request(url: "https://my-server1.corp/foo/bar",
                   method: .POST,
                   tlsConfiguration: specialServer1Settings)

[weissi]

Currently, the key is

    struct Key: Hashable {
        var scheme: Scheme
        var host: String
        var port: Int
        var unixPath: String

I think the only thing we'd need to do is add a var tlsConfiguration: TLSConfiguration? there (and make TLSConfigurable Hashable)

[weissi]

fixed with #358