fix(scripts): fix and refactor setup scripts

[hyperfinitism]

Purposes

• Fix path specification errors and early exit issues in make setup-nitro-cli
• Extract make download-root-ca from make setup-client as a separate target
• Ensure the downloaded certificate is reliably named root.pem

What's changed

• Update scripts/setup-nitro-cli.sh
  • Fix incorrect path references: ./build/install/etc/profile.d/... → /etc/profile.d/...
  • Prevent duplicate entries in $HOME/.bashrc by checking before appending
  • Fix early exit issue: nitro-cli-config -i internally calls exit, which was terminating the parent shell. Wrapped in a subshell with set +e ... set -e to allow the script to continue
• Update scripts/setup-client.sh
  • Remove root CA download logic (moved to download-root-ca.sh)
  • Simplify to only install Rust and dependencies
• Add scripts/download-root-ca.sh
  • Extract root CA download into a dedicated script
  • Improve reliability: extracts the .pem file from the downloaded zip and explicitly writes it to root.pem, regardless of the original filename inside the archive
• Update Makefile
  • Add download-root-ca target
  • Update help text to reflect the changes
• Update README.md
  • Update setup instructions to include the new make download-root-ca step
  • Clarify test environment details
  • Add AArch64 (m6g.xlarge) as a tested environment
  • Remove duplicate/redundant entries
• Update .gitignore
  • Add AWS_NitroEnclaves_Root-G1.zip and root.pem to ignore list

Testing

Tested on:

• Ubuntu 24.04 (x86_64) on c5.xlarge
• Ubuntu 24.04 (AArch64) on m6g.xlarge