feat: generate completion subcommand #1964

Job	Run time
Integration tests (macos-latest)	3m 52s
Unit tests (macos-latest, x86_64-apple-darwin, false)	4m 52s
Integration tests (ubuntu-latest)	2m 19s
Unit tests (windows-latest, x86_64-pc-windows-msvc, false)	4m 35s
Unit tests (ubuntu-latest, x86_64-unknown-linux-gnu, false)	2m 15s
Unit tests (ubuntu-latest, x86_64-unknown-linux-musl, true)	2m 44s
Rustfmt	12s
Unit tests (ubuntu-latest, i686-unknown-linux-gnu, true)	2m 33s
Unit tests (ubuntu-latest, arm-unknown-linux-gnueabihf, true)	2m 49s
Clippy	43s
Code coverage	2m 33s
Unit tests (ubuntu-latest, aarch64-unknown-linux-gnu, true)	2m 45s
	32m 12s

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