Rename debug_invalidate_system_caches_always to debug_discard_caches.
The name introduced by commit
4656e3d66 was agreed to be unreasonably
long. To match this change, rename initdb's recently-added
--clobber-cache option to --discard-caches.
Discussion: https://postgr.es/m/
1374320.
1625430433@sss.pgh.pa.us