CPack/DMG: Do not use CPACK_RESOURCE_FILE_LICENSE for SLA by default

Since macOS 12.0 deprecated the tools needed to attach a SLA to a
`.dmg`, we should no longer do this by default.  Add a policy to
change the default to off.

Fixes: #22978
59 jobs for !7176 with cpack-dmg-sla in 39 minutes and 51 seconds (queued for 6 seconds)
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