pgsql: Handle element label and label property objects in object addres

Handle element label and label property objects in object address functions

getObjectTypeDescription() and getObjectIdentityParts() do not handle
objects in pg_propgraph_element_label and pg_propgraph_label_property
catalogs. These functions when called for handling DDL that affects
these objects cause an "unsupported object class" error. An error is
reported when these functions are called via pg_identify_object() and
pg_identify_object_as_address() with objects from the said catalogs.

The objects in these catalogs do not have a (user-given) name but they
can be manipulated individually through ALTER PROPERTY GRAPH
sub-commands. Hence they need to be accessible to the event triggers.
Handle these catalogs in the respective functions.

Reported-by: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Author: Bertrand Drouvot <bertranddrouvot(dot)pg(at)gmail(dot)com>
Author: Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>
Reviewed-by: Michael Paquier <michael(at)paquier(dot)xyz>
Reviewed-by: Ashutosh Bapat <ashutosh(dot)bapat(dot)oss(at)gmail(dot)com>
Discussion: https://www.postgresql.org/message-id/aej1DkLwhyZWmtxJ@bdtpg

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/72498a86989e3491228ba09be43eab778a3ac943

Modified Files
--------------
src/backend/catalog/objectaddress.c | 89 ++++++++++
.../regress/expected/create_property_graph.out | 189 ++++++++++++---------
src/test/regress/expected/event_trigger.out | 22 +++
src/test/regress/expected/object_address.out | 9 +-
src/test/regress/sql/create_property_graph.sql | 31 ++--
src/test/regress/sql/event_trigger.sql | 15 ++
src/test/regress/sql/object_address.sql | 5 +-
7 files changed, 267 insertions(+), 93 deletions(-)