Add _INFO file validation

## Background
Currently, most fields of an _INFO file are not validated.

## Feature
Add _INFO file validation for Enceladus when Atum starts to support custom validators of _INFO files ([Atum/#22](https://github.com/AbsaOSS/atum/issues/22) and [Atum/#23](https://github.com/AbsaOSS/atum/issues/23))

## Here is the list of validations (to be extended)
- [x] Make sure 'Source' and 'Raw' checkpoints are present when Standardization starts.
- [ ] Country field should conform to the standardized list of countries (a MDR table).
- [ ] Source system name should be from the list of source system names (a MDR table).
- [ ] The information date should be in 'YYYY-MM-DD' format. Validate the date is the same as the report date
- [ ] Processing Start/Finish should be in a consistent format across checkpoints. Need to add validation of checkpoints created prior to Standardization.