Pin Rust toolchain, use Rustls (#679)

* Pin Rust toolchain and vendor OpenSSL

Based on our `flake.nix` file, it seems we have the following runtime dependencies: `openssl.out rocksdb git zlib nsync onnxruntime14`. Judging from our own `Cargo.lock`, and examining qdrant's `Cargo.lock`, we know that:

- [`rocksdb` is built statically and not needed at runtime](https://github.com/rust-rocksdb/rust-rocksdb/blob/master/librocksdb-sys/Cargo.toml#L16)  (unless provided by environment variables, which we don't do in default builds)
- [`zlib` is not used as default features are deactivated](https://github.com/qdrant/qdrant/blob/master/lib/segment/Cargo.toml#L28)
- [We removed `libgit2` in favor of `gitoxide`](#432)
- [We pin `onnxruntime` versions to specific binaries provided by `ort`](#231)

We also add a Rust toolchain configuration to pin the toolchain at `1.70.0`, and ensure that `openssl-sys` is built statically using the `vendored` feature.

This removes all remaining non-platform-specific runtime dependencies except `nsync`, which does not seem to be linked into either `bloop` builds or `qdrant`'s builds.

* Upgrade deps, use rustls

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Co-authored-by: rsdy <p@symmetree.dev>

Author: calyptobai