[execution-beacon] add ExtensionRef and RequestMirror HTTPRoute filter support

[0xDones]

execution-beacon

Description

• feat: align the httpRouteFilter schema with the Gateway API HTTPRouteFilterType set

values.schema.json only allowed four filter types, so a valid route using
ExtensionRef was rejected at render time:

- at '/HTTPRoute/rules/0/filters/0/type': value must be one of 'RequestHeaderModifier', 'ResponseHeaderModifier', 'RequestRedirect', 'URLRewrite'

The driving use case is attaching an NGINX Gateway Fabric SnippetsFilter
(group: gateway.nginx.org) to a route for API key auth.

Changes, scoped to charts/execution-beacon:

• httpRouteFilter.type enum extended with RequestMirror and ExtensionRef.
• New httpExtensionRef definition (group, kind, name — all required),
  modelled on Gateway API's LocalObjectReference.
• New httpRequestMirror definition with a backendRef (group, kind,
  name, namespace, port).
• additionalProperties: false kept on httpRouteFilter and on both new
  definitions.
• Chart version 3.1.0 -> 3.2.0 (additive, no breaking change).

templates/httproute.yaml needed no change — rule filters already pass through
via toYaml.

Verification

• Renders correctly for an ExtensionRef filter and for a RequestMirror filter.
• A rule combining all four pre-existing filter types still validates.
• Still rejected: an unknown type, an unknown key inside extensionRef, and
  extensionRef missing group.
• helm lint clean; helm unittest 28/28 pass; pre-commit hooks pass.

Note

bro-1322-reth-archive-node carries an unmerged breaking bump to 4.0.0. This PR
is independent of it, but whichever merges second will need its chart version
reconciled — if the reth work lands first, this becomes 4.1.0.

Notes

• I have read the CONTRIBUTING document.

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