pgsql: Add more LOG messages when starting and ending recovery from a b

Add more LOG messages when starting and ending recovery from a backup

Three LOG messages are added in the recovery code paths, providing
information that can be useful to track corruption issues depending on
the state of the cluster, telling that:
- Recovery has started from a backup_label.
- Recovery is restarting from a backup start LSN, without a
backup_label.
- Recovery has completed from a backup.

Author: Andres Freund
Reviewed-by: David Steele, Laurenz Albe, Michael Paquier
Discussion: https://postgr.es/m/20231117041811.vz4vgkthwjnwp2pp@awork3.anarazel.de

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/1d35f705e191581784e9df89bb69b7867ac9c342

Modified Files
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src/backend/access/transam/xlogrecovery.c | 34 +++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)