github/action: create a permanent 'latest' release

github/action: create a permanent 'latest' release

this commit extends the existing snapshot action to create a release named
'latest' with the built binaries for windows.

this 'latest' release will be updated after every push to github.

Change-Id: I75a64c598169241743add3ac9aa7a0337fbab7f2
Signed-off-by: Tarek BOCHKATI <tarek.bouchkati@gmail.com>
Reviewed-on: http://openocd.zylin.com/6127
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>