Move SDL usage code example

Move SDL usage code example

Move SDL usage code example from sdlgo repo's root to example
sub-directory and change it to be a runnable application. Earlier
example was belonging to the Golang test package what caused it to be
ran when 'go test ./...' -command was executed and execution of the
example was failing if DBAAS connection was missing. Execution failure
is also visible in the sdlgo coverage test of the sonarcloud.io.

Issue-Id: RIC-875

Signed-off-by: Timo Tietavainen <timo.tietavainen@nokia.com>
Change-Id: I6d980e0730d4a6f768448134bc7efece050a6d89