PEtab yaml file schema missing / broken links

[dweindl]

• Add PEtab 2.0 draft #554 accidentally modified the v1 schema instead of adding the v2 schema
• dead link to schema at https://petab.readthedocs.io/en/latest/v2/documentation_data_format.html#yaml-file-for-grouping-files
• dead link to schema at https://petab.readthedocs.io/en/latest/v1/documentation_data_format.html#yaml-file-for-grouping-files