[FEATURE] Add a plugin unit test to validate the json event schema

[jzonthemtn]

Is your feature request related to a problem?

Add a plugin unit test to validate the json event schema.

What solution would you like?

During the build, the UBI schema should validate against sample events.

For more reference, see the previous issue at o19s/opensearch-ubi#179 (comment).

[dblock]

[Catch All Triage - Attendees 1, 2, 3, 4, 5]