Library to connect to a pg-backup-api server.

Module to provide communication with a server in order to send new
tasks and query them.

pg-backup-api is a REST api that at the moment, is integrated with
barman only, and can provide a communication interface in order to
perform remote recoveries through background tasks. There are cases
where instead of writing a new repmgr module of some feature that
exists in backup tools already, like barman, pg-backup-api can
provide that integration.

repmgr.h

@@ -116,6 +116,7 @@
 #define DEFAULT_STANDBY_FOLLOW_TIMEOUT       30  /* seconds */
 #define DEFAULT_STANDBY_FOLLOW_RESTART       false
 #define DEFAULT_SHUTDOWN_CHECK_TIMEOUT       60  /* seconds */
+#define DEFAULT_STANDBY_PG_BACKUPAPI_OP_TYPE "recovery"
 #define DEFAULT_STANDBY_RECONNECT_TIMEOUT    60  /* seconds */
 #define DEFAULT_NODE_REJOIN_TIMEOUT          60  /* seconds */
 #define DEFAULT_ARCHIVE_READY_WARNING        16  /* WAL files */