nixos/security.pki: handle PEMs w/o a final newline
nixos/security.pki: handle PEMs w/o a final newline

According to the ABNF grammar for PEM files described in [RFC
7468][1], an eol character (i.e. a newline) is not mandatory after the
posteb line (i.e. "-----END CERTIFICATE-----" in the case of
certificates).

This commit makes our CA certificate bundler expression account for
the possibility that files in config.security.pki.certificateFiles
might not have final newlines, by using `awk` instead of `cat` to
concatenate them. (`awk` prints a final newline from each input file
even if the file doesn't end with a newline.)

[1]: https://datatracker.ietf.org/doc/html/rfc7468#section-3

NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs,NixOS/nixpkgs