Option to accept self-signed/invalid SSL certificates

[ChadThackray]

Problem

When running Transmission behind a reverse proxy with a self-signed certificate, TrguiNG cannot connect because the reqwest client performs strict certificate validation against the system trust store.

The connection fails with the equivalent of: SSL certificate problem: unable to get local issuer certificate

The predecessor (transgui) did not perform certificate validation at all, so these setups worked out of the box.

Proposal

Add a per-connection toggle to accept invalid/self-signed certificates.

Happy to submit a PR for this if approved.

[qu1ck]

Good idea, PR welcome.
I'm assuming you will create a separate cached client built with tls_danger_accept_invalid_certs which will be used for connections with corresponding option enabled.