Disallow negative values for max_retention_duration.

Disallow negative values for max_retention_duration.

The subscription option max_retention_duration accepts an integer value
representing a timeout in milliseconds, where zero means unlimited
retention (no timeout).  Negative values have no useful meaning, but were
silently accepted and stored in the subscription catalog.

A negative value causes should_stop_conflict_info_retention() to always
return true, because TimestampDifferenceExceeds() treats a negative
threshold as already exceeded.  This stops dead tuple retention
immediately rather than honoring the configured timeout.

Fix by rejecting negative values for max_retention_duration during CREATE
SUBSCRIPTION and ALTER SUBSCRIPTION.

Author: Chao Li <lic@highgo.com>
Reviewed-by: Hayato Kuroda <kuroda.hayato@fujitsu.com>
Reviewed-by: Amit Kapila <amit.kapila16@gmail.com>
Discussion: https://postgr.es/m/9232401A-DEEE-49E1-9D11-D14A776DB82B@gmail.com