mdadm: use shared system-sendmail

[Ekleog]

Motivation for this change

Use system-sendmail introduced by (not-yet-merged) #49228. Thus this PR is based on it, and currently the overall diff includes lots of useless things. The last commit is the only one important here.

This shares more code across nixpkgs. Hopefully other packages will follow.

Also noticed that mdadm currently had no maintainer, and added myself as one, so that someone feels responsible for future updates.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Fits CONTRIBUTING.md.

---

[GrahamcOfBorg]

Success on x86_64-linux (full log)

Attempted: mdadm, opensmtpd

Partial log (click to expand)

shrinking /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0/sbin/mdmon
shrinking /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0/sbin/mdadm
gzipping man pages under /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0/share/man/
strip is /nix/store/vcc4svb8gy29g4pam2zja6llkbcwsyiq-binutils-2.30/bin/strip
stripping (with command strip and flags -S) in /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0/lib  /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0/sbin
patching script interpreter paths in /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0
checking for references to /build in /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0...
moving /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0/sbin/* to /nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0/bin
/nix/store/hfxq5p84xi6m8lhl0d92jgp5hmvdgl5s-mdadm-4.0
/nix/store/qwd5xz5k043v5v11xm90zjkmpsnphj3v-opensmtpd-6.4.0p1

[GrahamcOfBorg]

Success on aarch64-linux (full log)

Attempted: mdadm, opensmtpd

Partial log (click to expand)

shrinking /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0/sbin/mdmon
shrinking /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0/sbin/mdadm
gzipping man pages under /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0/share/man/
strip is /nix/store/p9akxn2sfy4wkhqdqa3li97pc6jaz3r1-binutils-2.30/bin/strip
stripping (with command strip and flags -S) in /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0/lib  /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0/sbin
patching script interpreter paths in /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0
checking for references to /build in /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0...
moving /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0/sbin/* to /nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0/bin
/nix/store/0hdyyqclpm1lr922klq2m7szxs8pg8m8-mdadm-4.0
/nix/store/ihdq6cklcsdnkac9x6ly2y5r8bir707a-opensmtpd-6.4.0p1