[enhancement]: Support fastjsonschema as well as jsonschema for schema validator

[ani-sinha]

Enhancement

In RHEL, we are looking to drop support for jsonschema. We would like to use fastjsonschema. The api doc is here: https://horejsek.github.io/python-fastjsonschema/

It would be nice if cloud-init could support both python libraries to check json schema.

[blackboxsw]

Good suggestion @ani-sinha, I can see it packaged in alpine, rawhide, fedora, debian and ubuntu archives as well so making this switch should be desired for distributions which have this package available. This will be a fairly complex bit of work because cloudinit.config.schema has some tight coupling with the following for custom extensions:

• jsonscheme.ValidationError
• jsonschema.Draft4Validator, FormatChecker
• jsonschema.exceptions.best_match, SchemaError
• jsonschema.validators.create

But, this is definitely something worth exploring further to size this amount of effort.