See merge request !1268

When using pre-commit hook (the one installed by using `npm install`
from the root of the repository), all .json files are checked to be
valid json and formatted according to the ./format-json rules.

These templates were problematic for this script because they are not
really valid json, so name them .json.jinja2 instead of .jinja2.json so
that they are not selected by the pre-commit hook

See merge request nexedi/slapos!1262

See merge request nexedi/slapos!1267

Move hardcoded values to default values.
Source the whole content of the data-to-vm parameter.

See merge request nexedi/slapos!1266

This take another approach at c5cd4e06 (component/glib: set --with-python
to generate scripts with slapos python, 2022-09-20) because this python
might exceed the limit of shebang lines, that change was bad because it
brought back the problem that we fixed in 6acdc8ca (glib: put the expected
python in $PATH, 2019-12-18)

Now that component/defaults.cfg set the ${python:location}/bin in $PATH,
we can assume that python is always in $PATH. The problem with python3
software is that python3 does not install a "python" binary, only python3,
so we can use the $PYTHON environment variable which will be set to
python2 or python3 and that in both cases this will be a valid python
interpreter.

This re-applies 7581b668 (component/glib: remove bad file bin/gtester-report
after compilation, 2020-08-07) because with this approach that script's
shebang is just #!python3