feat: supprot OPA plugin complex response

[bzp2010]

What this PR does / why we need it:

Enhance OPA plug-in functionality to support overwriting of status codes, response headers, and response bodies when validation is rejected.

stage 2 of #5714

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?
• Is this PR backward compatible? If it is not backward compatible, please discuss on the mailing list first

[bzp2010]

Summary

The OPA plugin is enhanced in this PR to support overriding the status code, request header and request body in case of a failed check.

• Update OPA policy
• Update plugin

Description

A response containing the following can be sent to APISIX in the OPA policy.

{
  "result": {
    "allow": false,
    "status_code": 302,
    "headers": {
      "Location": "http://example.com/auth"
    },
    "reason": {
      "test": "test"
    }
  }
}

The status code, response header, and reason are all optional respectively, and the reason can be a string or object, and the plugin will automatically JSON encode according to the data type.

[bzp2010]

ping @shuaijinchao PTAL thanks

[anderseknert]

👏