Update version to 0.1.2 and enhance command line arguments

- Bump `gatekeeper` version to 0.1.2 in `Cargo.toml` and `Cargo.lock`.
- Add new command line arguments for upstream idle timeout and HTTP/2 support in the `Gateway` struct.
- Refactor proxy logic to conditionally set HTTP version and idle timeout based on new arguments.

Add integration tests for HTTP proxy functionality

- Introduce new integration tests for the HTTP proxy, covering scenarios such as proxying requests to multiple upstreams, handling TLS connections, and performing health checks.
- Update `Cargo.toml` to include `reqwest` and `tokio` as development dependencies.
- Remove empty `.gitkeep` file from the tests directory.
- Update `Cargo.lock` with new dependencies and versions.

Add ARM64 Linux Musl support