fix: enable hard navigate on 404

[abvthecity]

Related to #71194 and #71193

Additional feature flag that will enable hard navigate on /404 routes.

Why

Given the following proxy setup:

rewrites:
 - source: /(!?internal/):path*
   destination: https://another-nextjs-site.vercel.app/:path*

the client-side router is unaware that /internal/* belongs to the parent, and will render a 404 page.

How

Adding a hardNavigate404=true flag will always hard navigate on 404.

[ijjk]

Allow CI Workflow Run

• approve CI run for commit: 062c793

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[ijjk]

I'm thinking instead of hard-coding this behavior to /404 if we provide an experimental config to allow providing custom paths to the client router filter which allows specifying paths/partial paths that should trigger hard navigations.

x-ref:

next.js/packages/next/src/lib/create-client-router-filter.ts

Line 12 in d31b8b8

export function createClientRouterFilter(