feat(http): allow forceContentNegotiationTo to be a function

[RomainLanz]

Hey there! 👋🏻

This PR allows us to use a function instead of hardcoding a string for the forceContentNegotiationTo options.
It can be helpful when you have an application doing SSR & having some API routes that need to be forced to JSON.

Something similar is already done inside the shield module.

exceptRoutes: ({ request }) => request.url().includes('/api'),

[targos]

Should we await the result of the function (I don't know if it makes sense for this one to be implemented as async)?

[RomainLanz]

It could make sense, but I believe we should not handle it.

Having an async function means there is some side-effect. If someone has this use-case, he would be better of creating a middleware instead of coding it inside the configuration.

[thetutlage]

Yeah, async within config is something I will avoid too. Should we close this PR then?

[RomainLanz]

This PR does not add the support for asyncconfiguration, so we are all good to go.

[carlmathisen]

Thank you guys - this is such a good addition! My main use case was the app being an API, with a few extra endpoints for an admin panel. To be able to flexibly configure forced JSON on /v1/api endpoints, similar to @RomainLanz's example was exactly what I needed, and I'm sure it will be useful for others too.