Add support for cache_miss_only to cli.commit()

While it might seem that using the path of the object to determine if the rule is applying only to cache misses isn't a good idea, it is actually the best compromise between ease of import/management in varnish itself and reduced need to review the schema for vcl objects.

The alternative route would be to add a further tag to the vcl object schema to incapsulate cache misses there rather than in the path itself.

I didn't feel it would add much clarity at the cost of a riskier transition, but I'm open to hear otherwise.

Bug: T317794