feat: support custom HTTP filter ordering

[zhaohuabing]

This PR allows users to adjust HTTP filter orders to suit their specific use cases. It also:

• adds a constraint limiting each EnvoyExtensionPolicy to have a maximum of 16 wasm/extproc extensions.
• Fixes the JSON tag in FilterPosition API

Note: this PR doesn't handle the ordering of individual wasm/extproc extensions. This will be addressed in a follow-up PR, as it involves API change and may need more discussion.

Related: https://github.com/envoyproxy/gateway/issues/2571 https://github.com/envoyproxy/gateway/pull/2993

[alexwo]

/retest

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 94.66667% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 66.94%. Comparing base (29946b0) to head (42c3626). Report is 134 commits behind head on main.

:exclamation: Current head 42c3626 differs from pull request most recent head e4f6a93. Consider uploading reports for the commit e4f6a93 to get more accurate results

Files	Patch %	Lines
internal/xds/translator/httpfilters.go	93.54%	2 Missing and 2 partials :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3273      +/-   ##
==========================================
+ Coverage   66.51%   66.94%   +0.42%     
==========================================
  Files         161      163       +2     
  Lines       22673    23370     +697     
==========================================
+ Hits        15080    15644     +564     
- Misses       6720     6816      +96     
- Partials      873      910      +37     

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[arkodg]

Do we need to validate that we don't have cycles like:

  spec:
    filterOrder:
      - name: envoy.filters.http.jwt_authn
        before: envoy.filters.http.cors
      - name: envoy.filters.http.cors
        before: envoy.filters.http.jwt_authn

imo if we apply in order, we wont hit this issue, right ?

[zhaohuabing]

Do we need to validate that we don't have cycles like:

  spec:
    filterOrder:
      - name: envoy.filters.http.jwt_authn
        before: envoy.filters.http.cors
      - name: envoy.filters.http.cors
        before: envoy.filters.http.jwt_authn

imo if we apply in order, we wont hit this issue, right ?

Added a check for a more friendly UI.