enhancement: support request body matching in Gateway API and ApisixRoute

[kayx23]

Summary

Please triage whether the controller should support request body matching for routing.

Current behavior

APISIX itself supports body-aware matching through route vars / expression-based conditions, including request body derived values such as post_arg_*, but the current controller models do not expose an equivalent surface.

From the current API model:

• ApisixRouteHTTPMatchExprSubject.Scope supports Header, Query, and Path
• there is no request body scope in the route match expression model
• Gateway API integration also does not expose request body matching through the current controller model

As a result, body-based routing use cases supported by APISIX cannot currently be expressed through the controller.

Use cases affected

• routing based on fields in POST form or JSON request bodies
• expressing body-based match conditions through ApisixRoute or Gateway API instead of falling back to a separate APISIX configuration path

Code context

• api/v2/apisixroute_types.go
• api/v2/shared_types.go

[coderabbitai]

🔗 Related PRs

#387 - feat: support skip gatewayapi v1alpha2 [merged]
#388 - fix: cannot use ingress when disabling gateway API [merged]

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