test_scripts/gnss_test: add a gnss test script

This is formated for the librem5 screen and can display position and
satellites S/N ratio. It can also interface with the gts1800 test fixture.

Signed-off-by: Angus Ainslie <angus@akkea.ca>
3 jobs for gnss-testing in 3 minutes and 31 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #317032
librem5
build:deb

00:01:25

 
  Test
passed #317033
librem5
test:download:deb

00:01:46

passed #317034
librem5
test:download:pip

00:02:05