pgsql: Make crash recovery ignore recovery_min_apply_delay setting.

Make crash recovery ignore recovery_min_apply_delay setting.

In v11 or before, this setting could not take effect in crash recovery
because it's specified in recovery.conf and crash recovery always
starts without recovery.conf. But commit 2dedf4d9a8 integrated
recovery.conf into postgresql.conf and which unexpectedly allowed
this setting to take effect even in crash recovery. This is definitely
not good behavior.

To fix the issue, this commit makes crash recovery always ignore
recovery_min_apply_delay setting.

Back-patch to v12 where the issue was added.

Author: Fujii Masao
Reviewed-by: Michael Paquier
Discussion: https://postgr.es/m/CAHGQGwEyD6HdZLfdWc+95g=VQFPR4zQL4n+yHxQgGEGjaSVheQ@mail.gmail.com
Discussion: https://postgr.es/m/e445616d-023e-a268-8aa1-67b8b335340c@pgmasters.net

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/03666dfa1817ef602ef982a766b983efd43c460f

Modified Files
--------------
doc/src/sgml/config.sgml          | 3 ++-
src/backend/access/transam/xlog.c | 4 ++++
2 files changed, 6 insertions(+), 1 deletion(-)