switch to go:embed

[cyphar]

The internet requirement of the validate subcommand has been a fairly regular annoyance when using this tool in CI jobs and the like (where it's possible for the GET to fail intermittently), not to mention that it means you can't do any config validation in an air-gapped setup.

In the past, using gojsonschema's support for embedded data was ruled out because it was too annoying to maintain, but now that Go 1.16 has the embed package with //go:embed it seems that we should be able to implement this in a fairly painless way.

[kolyshkin]

One problem is, the validation is done against a specific schema version. Which one do we embed? Say we do latest tagged (1.0.2 for now). What if version in config differs? Do we require internet in this case? Should we fall back to validating against the version we have (with a warning)?

Related: I just found out that anything before 1.0.2 is not possible with latest gojsonschema, so it won't be possible to validate against spec < 1.0.2.

[kolyshkin]

Related: I just found out that anything before 1.0.2 is not possible with latest gojsonschema, so it won't be possible to validate against spec < 1.0.2.

See 61f09ec #733