[tz] Add new timezone for Hanoi Capital, Vietnam

[Steve Allen]

On Tue 2019-02-19T03:31:45+0700 KP hath writ:
> - GMT+0: July 1, 1906 to April 30, 1911 (Indochina)
> - GMT+7: May 1, 1911 (Indochina)
> - GMT+8: 23:00 December 31, 1942 (Indochina)
> - GMT+9: 23:00 on March 14, 1945 (Empire of Vietnam)
> - GMT+7: September 2, 1945 (Democratic Republic of Vietnam) and July 1,

BIH Bulletin Horaire indicates that Saigon was transmitting time signals
in 1924 and beginning with 1925 their reception times are tabulated.
An interesting note in Series 1 number 2 page 1 is that there was only
one transmitter so starting 1941-12-08 Saigon sacrificed time signals
for more important traffic.

--
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