allow initializing tls connector

[dr-bonez]

taking a tls connector as a type argument instead of mutating it later allows not setting a process-level CryptoProvider. Otherwise, you can end up with this nasty panic:

The application panicked (crashed).
Message:  no process-level CryptoProvider available -- call CryptoProvider::install_default() before this point
Location: /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/rustls-0.23.20/src/crypto/mod.rs:249