Expose {{.SelectedCommitRange}} to custom commands #6751

Job	Run time
check-codebase	12s
check-for-fixups	4s
build	1m 4s
check-required-label	3s
Integration Tests - git 2.20.0	1m 23s
lint	37s
Integration Tests - git 2.22.5	1m 8s
ci - ubuntu-latest	37s
Integration Tests - git 2.23.0	1m 23s
ci - windows-latest	3m 5s
Integration Tests - git 2.25.1	1m 11s
Integration Tests - git 2.30.8	1m 17s
Integration Tests - git latest	1m 17s
upload-coverage	14s
	13m 35s

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