This adds PostgreSQL 16 as a vendored postgresql version, and adapts the
code to support this version.
The important changes to PostgreSQL 16 compared to the PostgreSQL 15
changeset include the addition of a neon_rmgr instead of altering Postgres's
original WAL format.
Co-authored-by: Alexander Bayandin <alexander@neon.tech>
Co-authored-by: Heikki Linnakangas <heikki@neon.tech>
* Extract neon and neon_test_utils from postgres repo
* Remove neon from vendored postgres repo, and fix build_and_test.yml
* Move EmitWarningsOnPlaceholders to end of _PG_init in neon.c (from libpagestore.c)
* Fix Makefile location comments
* remove Makefile EXTRA_INSTALL flag
* Update Dockerfile.compute-node to build and include the neon extension
