`reqwest` dependency should have `default-features = false`

[matt-phylum]

Because Cargo does not have negative features, keycloak's dependency on reqwest without default-features = false causes a dependency on reqwest's default-tls feature, and crates dependent on keycloak cannot turn this dependency off if they don't want it.

[kilork]

Hi, thanks, this is very nice thing to have. We need to take next opportunity with version upgrade this, as it seems to me to be a breaking change.