Add a command to print the signature permission allowlist

This command can be used to print the signature permission allowlist for
a specific partition. The allowlist is a list of packages and the
permissions that they are allowed to hold. This command can be used to
report configuration and help debug any issues.

Bug: 336568924
Test: adb shell pm get-signature-permission-allowlist system
Change-Id: I8cc08595592e3997459f98cb082e26d843e0c8f1