Add `ostree admin post-copy` command #1912

Job	Run time
Build (Fedora)	1m 14s
Build (C9S)	1m 52s
build-integration	4m 53s
Code style	1m 6s
Build - FCOS minimal	2m 17s
Debian Stable with sign-ed25519 and FUSE 2	4m 41s
Debian Stable with curl, sign-ed25519, no gpgme, FUSE 3	3m 44s
Debian Stable 32 bit	4m 42s
Debian Stable without libsystemd	3m 51s
Debian Testing	5m 54s
Debian Testing with libsoup3	5m 17s
Debian stable + static-prepareroot	3m 50s
Ubuntu Latest Release	4m 39s
Privileged testing	47s
	48m 47s

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