Default json mime type on /api routes

[dargmuesli]

Initially, all routes that contained "api" were considered to have the json mime type (nuxt/nuxt#19093). Now, this behavior is changed to only check for routes starting with "api" (#971).
This discussion is meant to continue the conversation started on the related PRs and issues with the most recent comment being

Would you open an issue to discuss adding a .startsWith() test? We might also consider allowing handlers to indicate their preference somehow, or something else.

cc @danielroe @pi0

[dargmuesli]

For me personally the issue is fixed as routes starting with /api behave as before.

Nevertheless: In general, I'd expect throw createError statements in api routes to result in the json mime type, no matter how accessed. Reason being that I want to be able to reliably get the error message, even with custom fetch methods. As always, maybe there's a way I could achieve that goal in another way that currently just does not come to my mind right now.
That also means that I do not expect all api routes to be of json mime type per default, although that would be fine for me.

In the end, I think, the discussion boils down to the question whether the /api route should be opinionated to behave in its current special way. I'm fine with that.