cli/request: support passing instance parameters from a file
Support a syntax like:
slapos request \
--node=computer_guid=local \
--parameters-file=~/request.json \
ERP5 \
https://lab.nexedi.com/nexedi/slapos/raw/1.0.145/software/erp5/software.cfgto request an instance with parameters in ~/request.json file.
This also teach slapos.core about the instance schema, which makes it possible to
understand the serialisation, so that we no longer need to use _ = json.dump(params)
to encode parameters.
This also emits a warning when requesting with parameters which do not match the schema.