Replace `curl` with `reqwest`

[szokeasaurusrex]

The Sentry CLI currently uses curl to make requests to the Sentry API. The curl library simply provides bindings over the libcurl API.

We should replace curl with reqwest, which is a more popular alternative that does not depend on libcurl. This way, our build dependencies can be kept in Rust, which would reduce overhead with builds.

ref: #1798