disable reqwest default-tls

[jxs]

Hi, this allows not pulling the hyper-tls and its openssl-sys dependency and use rustls instead by downstream crates.
Thanks

[ralexstokes]

hi @jxs thanks for this!

do you have a link to any description of the problem? I know lighthouse had some issue here so maybe you can just link to a relevant PR?

[jxs]

Hi Alex.
We are currently trying to reduce Lighthouse's compilation time, hyper-tls and namely openssl-sys (due to static linking of openssl) is one of the biggest bottlenecks, one can confirm by running cargo build --release --timings.

After merging sigp/lighthouse#4650 and aligning reqwest's version we can now switch to rustls and not depend on
hyper-tls. But beacon-api-client depends on hyper-tls by default and in a non modifiable way which makes all downstream crates still need to fetch and compile hyper-tls.
This PR fixes that by allowing downstream crates to chose their tls flavour and for Lighthouse not pull hyper-tls and openssl-sys while still offering it as the default.

[ralexstokes]

makes sense! thanks for the explanation