pgsql: doc: Add timeline as valid recovery target in standby.signal doc

doc: Add timeline as valid recovery target in standby.signal documentation

The documentation states that no target settings will be used when
standby.signal is present, but this is not quite the case since
recovery_target_timeline is a valid recovery target for a standby.

Update the documentation with this exception.

Author: David Steele <david@pgmasters.net>
Discussion: https://www.postgresql.org/message-id/flat/e445616d-023e-a268-8aa1-67b8b335340c%40pgmasters.net

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a37980d4282436b4019a8e427b02919b04cb625a

Modified Files
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doc/src/sgml/config.sgml | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)