BUR #27116 has been approved by @nonamethanks.
rename east_german -> east_germany
create alias german_democratic_republic -> east_germany
The tag "East German" is always used for the former country of East Germany, so naming it only as "East German" is quite misleading, since it may also means the distinct eastern German culture. Since the tag West Germany exists, I see no reason to allow this inconsistency any further.
Also added the "German Democratic Republic" alias for some people who may search with the official name instead.