Provide rpm/deb package for arm64 and aarch64

What does this MR do?

Provides rpm/deb packages for arm64. Example release index containing arm64 .deb/.rpm: https://gitlab-runner-downloads.s3.amazonaws.com/4872-arm64-deb-rpm/index.html

Why was this MR needed?

See #4872 (closed).

Are there points in the code the reviewer needs to double check?

• I added && fpm --help 1>/dev/null to the package-deps target because I ran into issues on my system, where I did have an fpm symlink, but it was a non-working one. This way the script will detect that situation and reinstall the gem if needed.
• I added an initial commit to fix some indentation issues in ci/package, replace which usage with the standard equivalent command -v, and quote an array expansion to avoid re-splitting elements.

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

Closes #4872 (closed) Closes #3435 (closed)