mon: Rename main script to "op5"
This command line tool being named "mon" is a bit strange, and
also troublesome, which has been pointed out among the comments
of #7244 for example.
Keeping "mon" as a symlink to "op5" means that everything should
continue working as usual.
One day, all op5 related command line tools will hopefully be
grouped together and accessible via this one and only "op5" tool...
Change-Id: Iafc81c17c81fc5199965c166ca84df64864507ae
Signed-off-by: Philip Eklöf <peklof@op5.com>