Revert #7316

[carodewig]

This PR reverts #7316 which moved the router's content negotiation to a plugin.

Moving the logic led to unintended side effects, including not allowing users to set custom accept headers on requests and content types on responses.

Fixes #7555

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[abernix]

@carodewig do you agree this "Fixes #7555", too?

[carodewig]

@carodewig do you agree this "Fixes #7555", too?

@abernix Yes it will, good catch!