pgsql: Allow setting failover property in the replication command.

Allow setting failover property in the replication command.

This commit implements a new replication command called
ALTER_REPLICATION_SLOT and a corresponding walreceiver API function named
walrcv_alter_slot. Additionally, the CREATE_REPLICATION_SLOT command has
been extended to support the failover option.

These new additions allow the modification of the failover property of a
replication slot on the publisher. A subsequent commit will make use of
these commands in subscription commands and will add the tests as well to
cover the functionality added/changed by this commit.

Author: Hou Zhijie, Shveta Malik
Reviewed-by: Peter Smith, Bertrand Drouvot, Dilip Kumar, Masahiko Sawada, Nisha Moond, Kuroda, Hayato, Amit Kapila
Discussion: https://postgr.es/m/514f6f2f-6833-4539-39f1-96cd1e011f23@enterprisedb.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/73292404370c9900a96e2bebdc7144f7010339cf

Modified Files
--------------
doc/src/sgml/protocol.sgml                         | 50 +++++++++++++++++
src/backend/commands/subscriptioncmds.c            |  2 +-
.../libpqwalreceiver/libpqwalreceiver.c            | 44 ++++++++++++++-
src/backend/replication/logical/tablesync.c        |  1 +
src/backend/replication/repl_gram.y                | 20 ++++++-
src/backend/replication/repl_scanner.l             |  2 +
src/backend/replication/slot.c                     | 25 +++++++++
src/backend/replication/walreceiver.c              |  2 +-
src/backend/replication/walsender.c                | 62 ++++++++++++++++++++--
src/include/nodes/replnodes.h                      | 12 +++++
src/include/replication/slot.h                     |  1 +
src/include/replication/walreceiver.h              | 18 ++++++-
src/tools/pgindent/typedefs.list                   |  2 +
13 files changed, 230 insertions(+), 11 deletions(-)