build: allow to use rustls instead of native-tls

[FlorentinDUBOIS]

• This is used in an effort to remove all dependencies to openssl. Which could be interesting in embedded system or on environment which is difficult to know on which openssl version the software will run it and breaks deployments.
• It introduces two compiler feature flags which are tokio-rustls-runtime and async-std-rustls-runtime that have the same meaning as tokio-runtime and async-std-runtime except that they use rustls.
• There is a safe guard, if we enable both runtimes, this is the native-tls ones that are used to keep consistent with the current behaviour.

[FlorentinDUBOIS]

Hello @tisonkun :wave:, long time no see ! I made some changes to allow to use rustls instead of native-tls using compiler feature flags. Could you give me your thought of this pull request ?

To give you more context about this pull request, at Clever Cloud, we are doing cross-compiling stuffs and some times build statically binaries and it will helps us, if we could remove the dependency to openssl to do so.

[FlorentinDUBOIS]

By the way, I have updated all dependencies !

[FlorentinDUBOIS]

Hello @tisonkun and @CleverAkanoa, I have deployed this patch in production and it works pretty well.

[tisonkun]

Thank you! I'll review this patch in days.

[FlorentinDUBOIS]

I am glad that you are ok with those modification, I will do the modification above about the hyphen and I will add the compile time error as well. By the way, once this will be merged I will rebase the pull request #267 to integrate those changes.

[FlorentinDUBOIS]

Hey @tisonkun, I did the modification, could you check that everything is ok for you ?

[FlorentinDUBOIS]

As @CleverAkanoa and @tisonkun approve this pull request, I merge it.