Add command to open git difftool #5137

Job	Run time
build	1m 31s
Integration Tests - git 2.20.0	1m 8s
check-codebase	21s
check-required-label	2s
lint	25s
Integration Tests - git 2.22.5	1m 3s
Integration Tests - git 2.23.0	1m 11s
Integration Tests - git 2.25.1	1m 11s
ci - ubuntu-latest	34s
ci - windows-latest	2m 43s
Integration Tests - git 2.30.8	1m 18s
Integration Tests - git latest	1m 20s
upload-coverage	9s
	12m 56s

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