Implement type validation in conf

[phorward]

In the longer term, we could also look to validate the values in setattr against the type hints.

Originally posted by @sveneberth in #1106 (comment)

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There're already some checks that can be improved

I think this check could be moved to a better place where it is not called on every request. But okay for main. On develop, we can validate it in the config object.

Originally posted by @sveneberth in #1106 (comment)