postgres_fdw: Replace WAIT_EVENT_EXTENSION with custom wait events
Three custom wait events are added here:
- "PostgresFdwCleanupResult", waiting while cleaning up PQgetResult() on
transaction abort.
- "PostgresFdwConnect", waiting to establish a connection to a remote
server.
- "PostgresFdwGetResult", waiting to receive a result from a remote
server.
Author: Masahiro Ikeda
Discussion: https://postgr.es/m/
197bce267fa691a0ac62c86c4ab904c4@oss.nttdata.com