feat: Values object can be used in payload of generic contextualizer and remote authorizer

[dadrus]

Related issue(s)

closes #686

Checklist

• I agree to follow this project's Code of Conduct.
• I have read, and I am following this repository's Contributing Guidelines.
• I have read the Security Policy.
• I have referenced an issue describing the bug/feature request.
• I have added tests that prove the correctness of my implementation.
• I have updated the documentation.

Description

Makes following possible:

- id: openfga
  config:
    endpoint: # etc.
    payload: |
      {
        "user": "user:{{ .Subject.ID }}",
        "relation": {{ quote .Values.relation }},
        "resource": {{ quote .Values.resource }}
      }

and then used in a pipeline like

- authorizer: openfga
  config:
    values:
      relation: read
      resource: "endpoint:foo"

which will result in the following json payload sent to the defined endpoint for the .Subject.ID being 1:

{
    "user": "user:1",
    "relation": "read",
    "resource": "endpoint:foo"
}

If the values property is defined in the configuration of the particular mechanism, the corresponding entries act as defaults for the rule pipeline making use of that mechanism.

[codecov]

Codecov Report

Merging #749 (a9130ac) into main (9809fe4) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #749   +/-   ##
=======================================
  Coverage   89.59%   89.59%           
=======================================
  Files         215      215           
  Lines        9227     9229    +2     
=======================================
+ Hits         8267     8269    +2     
  Misses        767      767           
  Partials      193      193           

Impacted Files	Coverage Δ
.../rules/mechanisms/authorizers/remote_authorizer.go	83.33% <100.00%> (+0.05%)	⬆️
...chanisms/contextualizers/generic_contextualizer.go	86.85% <100.00%> (+0.05%)	⬆️

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more