Update test harness to include flag metadata

[toddbaert]

With this schema change, flag metadata can now be stored in flag configuration files. Specifically, these can contain things like version and flag set id information so that consumers can use this data in flag evaluations, caching, telemetry etc.

We need to add e2e tests that assert the presence of this metadata

Acceptance criteria:

• add metadata to one of the test flag-sets, probably the testing-flags is best:

  flagd-testbed/flags/testing-flags.json

  Line 2 in e132d25

  "flags": {

• add some additional gherkin in the flagd test set that asserts the addition of this metadata when some new "metadata-test-flag" is added