Add initial Copilot instructions #3925

Job	Run time
Resolve environment (ubuntu-latest, default)	32s
Resolve environment (ubuntu-latest, linked)	36s
Resolve environment (macos-latest, default)	1m 40s
Resolve environment (macos-latest, linked)	2m 37s
Resolve environment (windows-latest, nightly-latest)	2m 24s
Resolve environment (windows-latest, default)	2m 25s
Resolve environment (windows-latest, linked)	2m 27s
Resolve environment (macos-latest, nightly-latest)	2m 34s
Resolve environment (ubuntu-latest, nightly-latest)	33s
	15m 48s

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