pgsql: Allow background workers to bypass datallowconn

Allow background workers to bypass datallowconn

THis adds a "flags" field to the BackgroundWorkerInitializeConnection()
and BackgroundWorkerInitializeConnectionByOid(). For now only one flag,
BGWORKER_BYPASS_ALLOWCONN, is defined, which allows the worker to ignore
datallowconn.

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/eed1ce72e1593d3e8b7461d7744808d4d6bf402b

Modified Files
--------------
contrib/pg_prewarm/autoprewarm.c           |  2 +-
src/backend/access/transam/parallel.c      |  3 ++-
src/backend/bootstrap/bootstrap.c          |  2 +-
src/backend/postmaster/autovacuum.c        |  4 ++--
src/backend/postmaster/postmaster.c        |  8 ++++----
src/backend/replication/logical/launcher.c |  2 +-
src/backend/replication/logical/worker.c   |  3 ++-
src/backend/tcop/postgres.c                |  2 +-
src/backend/utils/init/postinit.c          | 10 +++++-----
src/include/miscadmin.h                    |  2 +-
src/include/postmaster/bgworker.h          |  7 +++++--
11 files changed, 25 insertions(+), 20 deletions(-)