Fix/prevent unhandled promise rejections in Vue components

As mentioned in #335530 (comment 730596869), we have a number of components where request errors are not handled, or are rethrown and then not handled).

These are effectively unhandled promise rejections, although probably the UX is unaffected, as at least in most cases the catch block does handle the error, it happens to also rethrow it.

For now this is an issue, but it will probably need to be promoted to an epic to fix all instances and add documentation/linting to avoid this in future.