fix(Makefile): fix bundle validation by fetching/supplying definitions schema

[vdice]

Now that the bundle schema references the new definitions.schema.json, we need to fetch this referenced schema and supply it to the ajv cli for validation. (This manual step is needed until cnabio/cnab.io#15 is closed.)

[carolynvs]

This looks good but I was hoping to see publishexamplebundles pass on the PR. It doesn't seem to have run though?

[vdice]

@carolynvs previously/currently we only publish bundles on merges to master. Perhaps the thinking was we might not want to publish them from some/all PRs. We can update the logic to run that task on PRs, though. WDYT?

(We do still run validation on the bundles on PRs; it's the validate check, e.g. https://github.com/deislabs/porter/pull/581/checks?check_run_id=212309404 / https://brigadecore.github.io/kashti/jobs/porter-validate-01dkywajb6e3pa10eyk7jg7fsz)

[carolynvs]

Thanks! I was looking for validate. 👍