Update/fix TLS and https

[MagnusS]

After we updated the build system TLS and https have not been working and the libraries we previously used (openssl, s2n, botan2) still build, but they have not been updated to the latest versions. Botan2 is now end of life.

We should consider whether we need all these three libraries (perhaps e.g. s2n is enough) - then update to the latest version and fix the https/tls code.

[mazunki]

Slightly related: we should really find a better name for either this TLS (transport-layer security) or for the other TLS (thread-local storage). Having the same name for both is definitely confusing.