Following up on #543 and the discussion during the last PEtab editor meeting:
There was general consent to allow using observableIDs in the `noiseFormula` column in the observables table.

What was not discussed explicitly:
* Should all observable IDs be allowed, or only the current one?
* If so, should it be allowed to use observable IDs inside `observableFormula`?

CC @PEtab-dev/petab-editors

Closes ##543