Building chain.pem, fullchain.pem and all.pem was implemented seven times across three task files with
identical stat, awk and copy tasks. The blocks now include tasks/concatenate.yaml and pass the sources, the
destination and the mode, which removes about a hundred lines.
Two side effects come with it. Every source file is checked instead of only the foreign one, so a missing
file skips the block instead of letting awk fail. And the trailing newline of the result is kept, because
stdout_lines joined by a newline dropped it.
Co-authored-by: Copilot <copilot@github.com>
