Add Rust-based rabbitmqadmin-ng and remove Python

The RabbitMQ management images now include the Rust-based
`rabbitmqadmin-ng` CLI tool when possible. The deprecated Python version
of `rabbitmqadmin` will no longer be available.

This change adds a two-stage build to `Dockerfile-management.template`:
- **Download stage**: Attempts to download `rabbitmqadmin-ng` from
  GitHub release for the target architecture on Ubuntu only.
- **Final stage**: Copies the Rust binary if download succeeded.

The `versions.sh` script fetches the latest `rabbitmqadmin-ng` release
tag from the GitHub API and calculates SHA256 checksums and download
URLs for the release artifacts for x86_64 and aarch64 architectures.

Author: lukebakken

.gitignore

@@ -1 +1,4 @@
+*.tar.gz
+*.zip
+rustup-init.sh
 .jq-template.awk