pgsql: Allow dbname in pg_basebackup/pg_receivewal connstring

Allow dbname in pg_basebackup/pg_receivewal connstring

As physical replication work at the cluster level and not database
level, any dbname in the connection string is ignored. Proxies and
middleware used in connecting to the cluster might however need to
know the dbname in order to make the correct routing decision for
the connection.

With this the startup packet will include the dbname parameter.

Author: Jelte Fennema-Nio <me@jeltef.nl>
Reviewed-by: Tristen Raab <tristen.raab@highgo.ca>
Reviewed-by: Jim Jones <jim.jones@uni-muenster.de>
Discussion: https://postgr.es/m/CAGECzQTw-dZkVT_RELRzfWRzY714-VaTjoBATYfZq93R8C-auA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/cca97ce6a6653df7f4ec71ecd54944cc9a6c4c16

Modified Files
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doc/src/sgml/ref/pg_basebackup.sgml |  5 ++++-
doc/src/sgml/ref/pg_receivewal.sgml |  7 +++++--
src/bin/pg_basebackup/streamutil.c  | 29 ++++++++++++++++++-----------
3 files changed, 27 insertions(+), 14 deletions(-)