pgsql: Report missing wait event for timeline history file.

Report missing wait event for timeline history file.

TimelineHistoryRead and TimelineHistoryWrite wait events are reported
during waiting for a read and write of a timeline history file, respectively.
However, previously, TimelineHistoryRead wait event was not reported
while readTimeLineHistory() was reading a timeline history file. Also
TimelineHistoryWrite was not reported while writeTimeLineHistory() was
writing one line with the details of the timeline split, at the end.
This commit fixes these issues.

Back-patch to v10 where wait events for a timeline history file was added.

Author: Masahiro Ikeda
Reviewed-by: Michael Paquier, Fujii Masao
Discussion: https://postgr.es/m/d11b0c910b63684424e06772eb844ab5@oss.nttdata.com

Branch
------
REL_12_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/a354d015386a24bbe4cfcf21a983cf7a57ad89b1

Modified Files
--------------
src/backend/access/transam/timeline.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)