HTTPS requests are used to fetch
remote images in HTML emails,
to fetch autoconfig XML,
to POST requests for `DCACCOUNT:` QR codes
to make OAuth 2 API requests
and to connect to HTTPS proxies.
Rustls is more aggressive than OpenSSL
in deprecating cryptographic algorithms
so we cannot use it for IMAP and SMTP
to avoid breaking compatibility,
but for HTTPS requests listed
above this should not result in problems.
As HTTPS requests use only strict TLS checks,
there is no `strict_tls` argument
in `wrap_rustls` function.
Rustls is already used by iroh,
so this change does not introduce new dependencies.
This change introduces new config options
`proxy_enabled` and `proxy_url`
that replace `socks5_*`.
Tested with deltachat-repl
by starting it with
`cargo run --locked -p deltachat-repl -- deltachat-db` and running
```
> set proxy_enabled 1
> set proxy_url ss://...
> setqr dcaccount:https://chatmail.example.org/new
> configure
```
async-smtp does not implement read buffering anymore
and expects library user to implement it.
To implement read buffer, we wrap streams into BufStream
instead of BufWriter.
