Revert "postgresql: drop fallback for extra_headers in Revision.metadata"
This reverts commit 8435607b
There are still unmigrated extra_headers
in Revision.metadata. For example, swh:1:rev:04a3d20ff411409ab98474892b2bb1713bde0f7f
(this re-opens swh/infra/sysadm-environment#2564)
Edited by vlorentz