Add verification on source upload
When a source_manager uploads a source, there is currently no verification on the quality of the file and its content.
There is a need to explicitly explain where there are errors with warnings etc.
Verify:
- That the file is
json
- That the content follows IS standard
- That the mandatory variables are present
- That the variables from a controled list are correct
- That the variables type is correct (controled list, date, numeric, string)
- That the number of variable in a list follows its cardinality