Diag and data table schema updates

[uramirez8707]

1. Adds is_ocean as a valid optional key at the file level
2. Allow freq: 0 and freq: -1
3. Add restrictions to new_file_freq and file_duration
4. Make the reduction, module, and kind keys optional at the file level. If they are present at the file level, they are optional at the variable level, otherwise they are required. This is needed after Modern diag_manager: Simplify the diag table yaml FMS#1545
5. Only allow fregrid as the acceptable source for weight files