[RFC] add new libtls implementation

[ericonr]

Based on #21056 and some discussion in #20935

@leahneukirchen has suggested an alternative that is building only libtls from LibreSSL instead. I haven't tried this one yet.( See libressl/portable@fe42a80 )

My current propositions are:

• libretls from causal agency, who is the author of most of the software in our repos that depend on libtls
• libtls-bearssl, which is based on BearSSL instead of any sort of mix between LibreSSL/OpenSSL

[ericonr]

The libtls-standalone option is https://gitlab.alpinelinux.org/alpine/aports/-/blob/6012e47e379b125867e0dddada4ce1af2d589d5a/main/libtls-standalone/APKBUILD , but it is unmaintained (was only moved back to main because other things depend on it), and idk if all these workarounds are necessary with recent LibreSSL.

[leahneukirchen]

LibreSSL libtls: #28732

[ericonr]

Closing in favor of leah's approach.