opa: Update to 0.16.0

Changes:
0.61.0
------
This release contains a mix of new features and bugfixes.

Runtime, SDK
------------
- Adding `--v1-compatible` flag to all previously unsupported command line
  commands
- Don't load files in tarball exceeding `size_limit_bytes`
- Allow TLS cipher suites to be set for the OPA server
- Removing deprecated fields and functions related to rego-v1 compatibility

Topdown
-------
- topdown: Clean expired `http.send` cache entries periodically

(leot)