cli: Introduce `write_labeled!` template formatter macro #14587

Job	Run time
Build jj-lib without Git support	43s
cargo-deny (advisories)	21s
Check protos	25s
cargo-deny (bans licenses sources)	20s
build (ubuntu-latest)	4m 13s
build (macos-13)	6m 13s
build (macos-14)	3m 15s
Clippy check	2m 28s
Check that MkDocs can build the docs	24s
build (windows-latest)	10m 48s
Check that MkDocs can build the docs with Poetry 1.8	21s
build (ubuntu-latest, --all-features)	5m 27s
Check formatting	14s
	35m 12s

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