Validate schedule configurations for minLength/maxLength and pattern

[benoit74]

In the /offliners API, return minLength, maxLength and pattern. Adapt offliner definitions (new field type to create) so that these values can be sourced from the definitions and automatically provided in the API. In the UI, use these values to set them in the HTML5 elements and validate the input before submitting the form. Also adapt zimit-frontend to use these values (https://github.com/openzim/zimit-frontend/issues/41).