Add proper optic error reporting

[mikkeldenker]

If one tries to perform a search with an optic with syntax errors, the search fails and shows a 500 internal server error to the user without any details on what went wrong.
The parsing error should instead be properly propagated so the user can see exactly where the syntax error is.

I think we might need to change how non-ok responses are handled in abeye so we can properly catch and handle the errors (preamble.ts#L40-L49).
We will also somehow need to add the full parsing error to the body of the 400 http response from Stracts API, so this can be shown to the user.