Tiered rate limits with variables

[pdabelf5]

Proposed changes

Add the ability to add a condition to the rate limit Policy to allow users to rate limit on an NGINX variable. This can allow users to rate limit based on a variable containing a certain value. For example, rate limit all POST requests to 1 r/s, or if an API Key client name matches a specific regex.

Examples

apiVersion: k8s.nginx.org/v1
kind: Policy
metadata:
  name: rate-limit-premium
spec:
  rateLimit:
    rate: 1r/s
    key: ${apikey_client_name}
    zoneSize: 10M
    condition:
      variables:
        - name: $apikey_client_name
          match: "~^.*-premium$"
---
apiVersion: k8s.nginx.org/v1
kind: Policy
metadata:
  name: rate-limit-basic
spec:
  rateLimit:
    rate: 1r/s
    key: ${apikey_client_name}
    zoneSize: 10M
    condition:
      variables:
        - name: $apikey_client_name
          match: "~^.*-basic$"
      default: true

Closes #7868

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[github-actions]

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Name	Link
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[codecov]

Codecov Report

Attention: Patch coverage is 97.29730% with 4 lines in your changes missing coverage. Please review.

Project coverage is 52.92%. Comparing base (5f037b9) to head (2a1009a).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/apis/configuration/validation/common.go	0.00%	2 Missing ⚠️
pkg/apis/configuration/validation/policy.go	60.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7884      +/-   ##
==========================================
+ Coverage   52.82%   52.92%   +0.10%     
==========================================
  Files          90       90              
  Lines       21671    21732      +61     
==========================================
+ Hits        11447    11502      +55     
- Misses       9747     9751       +4     
- Partials      477      479       +2     

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[ADubhlaoich]

I've given edit suggestions for a lot of style errors in the API key README.

All of the feedback applies to the request method README, too.

• Incorrect product name (We never say just 'Ingress Controller')
• Unnecessary nesting
• Erroneous list numbering (Enumeration doesn't work in plain markdown)
• Title Case instead of sentence case
• Numbered headings