build(deps): bump openpolicyagent/opa from 0.56.0-istio to 0.57.0-ist…

…io in /examples/ext_authz (envoyproxy#29867)

build(deps): bump openpolicyagent/opa in /examples/ext_authz

Bumps openpolicyagent/opa from 0.56.0-istio to 0.57.0-istio.

---
updated-dependencies:
- dependency-name: openpolicyagent/opa
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

examples/ext_authz/Dockerfile-opa

@@ -1 +1 @@
-FROM openpolicyagent/opa:0.56.0-istio@sha256:b9c81ab586de93a52ff063ba92035fbca98b61ac40226a1aab482fb970b8c366
+FROM openpolicyagent/opa:0.57.0-istio@sha256:17ddd114d5277d6ddf1b402e5c3181ace6326abf6cb57724a585ff3b3551cee5