This is provided with a new switch --write-recovery-conf and reuses the
pg_basebackup code.

Author: Paul Guo, Jimmy Yih, Ashwin Agrawal
Reviewed-by: Alexey Kondratov, Michaël Paquier, Álvaro Herrera
Discussion: https://postgr.es/m/CAEET0ZEffUkXc48pg2iqARQgGRYDiiVxDu+yYek_bTwJF+q=Uw@mail.gmail.com