uhv: nghttp2 patch: add option to disable header validation

[ameily]

As part of the unified header validation component, nghttp2 will need to be modified at build time to include a new option that disables header validation on a per-request basis. This issue is similar to #19750, which is targeting HTTP 1 parsing. The intent is that nghttp2 will be configured to disable header validation when the UHV is being used.

The result will be a patch that is applied during the build. We could also potentially share the patch upstream if desired.

There is an existing option within nghttp2 to disable all http messaging mechanisms (nghttp2_option_set_no_http_messaging). However, that appears to be too heavy-handed and would affect larger portions of the h2 codec. The patch would most likely skip calls to nghttp_check_header_*() when loading the header.

[github-actions]

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[ameily]

With the recent move to oghttp2, we'll be closing our existing PR and opening a new one that targets oghttp2. Similar to H1, header validations for H2 will be disabled when the UHV compile time flag is enabled. We plan on using the new validate_http_headers exposed by the external_quiche_http2::adapter::OgHttp2Adapter::Options class, most likely within the Http2Options constructor.