feat: add Body scope to ApisixRoute match expressions for request body matching

[AlinsRan]

Summary

Add Body as a new scope value for ApisixRouteHTTPMatchExprSubject, enabling request body matching in ApisixRoute HTTP match expressions.

How it works

When scope: Body is used, the subject maps to APISIX's post_arg.<name> variable. This variable supports:

• application/json
• application/x-www-form-urlencoded
• multipart/form-data

Dot-notation JSON path expressions are also supported (e.g., model.version, messages[*].role).

Example:

exprs:
- subject:
    scope: Body
    name: action        # matches form field or JSON key
  op: Equal
  value: login

exprs:
- subject:
    scope: Body
    name: model.version  # dot-notation JSON path
  op: Equal
  value: gpt-4

Changes

• api/v2/shared_types.go: add ScopeBody = "Body" constant
• api/v2/apisixroute_types.go:
  • Add case ScopeBody in ToVars() mapping to post_arg.<name>
  • Add Body to +kubebuilder:validation:Enum on Scope field
  • Add +kubebuilder:validation:XValidation CEL rule: name is required when scope is not Path
  • Make Name field optional (omitempty) so Path scope works without providing a name
• api/v2/apisixroute_types_test.go: unit tests for Body scope and CEL validation
• config/crd/bases/apisix.apache.org_apisixroutes.yaml: regenerated
• docs/en/latest/reference/api-reference.md: regenerated
• test/e2e/crds/v2/route.go: e2e tests for urlencoded form field and JSON nested path matching

Testing

Unit tests:

go test ./api/v2/... -run "TestToVars|TestCEL"

E2e tests added:

• Test ApisixRoute match by body vars (urlencoded): POST form field action=login
• Test ApisixRoute match by body vars (JSON nested path): POST JSON {"model": {"version": "gpt-4"}} with model.version dot-notation