pg_dump: Allow dumping data of specific foreign servers

pg_dump: Allow dumping data of specific foreign servers

The new command-line switch --include-foreign-data=PATTERN lets the user
specify foreign servers from which to dump foreign table data.  This can
be refined by further inclusion/exclusion switches, so that the user has
full control over which tables to dump.

A limitation is that this doesn't work in combination with parallel
dumps, for implementation reasons.  This might be lifted in the future,
but requires shuffling some code around.

Author: Luis Carril <luis.carril@swarm64.com>
Reviewed-by: Daniel Gustafsson <daniel@yesql.se>
Reviewed-by: Surafel Temesgen <surafel3000@gmail.com>
Reviewed-by: vignesh C <vignesh21@gmail.com>
Reviewed-by: Álvaro Herrera <alvherre@2ndQuadrant.com>
Discussion: https://postgr.es/m/LEJPR01MB0185483C0079D2F651B16231E7FC0@LEJPR01MB0185.DEUPRD01.PROD.OUTLOOK.DE