Update 08-opa-envoy configuation

[PoisWu]

• Updated the envoy configuration from API V2 to V3
• Update JWTs in the README.md because the old ones are expired

[solo-build-bot[bot]]

Waiting for approval from someone in the solo-io org to start testing.

[peterj]

Looks good -- thanks for this PR. We've done a newer OPA episode as well here.

[PoisWu]

Thanks for telling me the release of newer OPA episode. It looks very interesting.