http: add server factory only factory support to dynamic_forward_proxy

[wbpcode]

Commit Message: http: add server factory only factory support to dynamic_forward_proxy
Additional Description:
This adds the server-factory-context-only filter factory creation method
(createHttpFilterFactoryFromProtoTyped taking only a ServerFactoryContext,
introduced in #45989) to the dynamic_forward_proxy HTTP filter(s).

This allows these filters to be created in contexts where only a
ServerFactoryContext is available (e.g. route/virtual-host level filter
configuration) rather than requiring the full downstream FactoryContext.
The existing downstream FactoryContext path is preserved and now delegates
to a shared helper, so behavior for existing use cases is unchanged.

Generative AI was used to assist with this change. I have reviewed all changes.
Risk Level: Low
Testing: Existing/added unit config tests; CI.
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A

[repokitteh-read-only]

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🐱

Caused by: #46222 was opened by wbpcode.

see: more, trace.