Add isCatalogRel in rmgrdesc

Hi hackers,

6af1793954 added a new field namely "isCatalogRel" in some WAL records
to help detecting row removal conflict during logical decoding from standby.

Please find attached a patch to add this field in the related rmgrdesc (i.e
all the ones that already provide the snapshotConflictHorizon except the one
related to xl_heap_visible: indeed a new bit was added in its flag field in 6af1793954
instead of adding the isCatalogRel bool).

I think it's worth it, as this new field could help diagnose conflicts issues (if any).

Looking forward to your feedback,

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com