User input validation / normalisation for strings?

[jluethi]

Following up on fractal-analytics-platform/fractal-web#824

Should we have some lightweight normalisation in Fractal tasks that normalises strings to e.g. remove trailing/leading whitespace? We could enforce more differentiable conditions on a task level. E.g. a label name cannot contain / or some other special characters either, while Fractal web needs to allow / in string inputs when paths are required