Split_data config

[peterdudfield]

Detailed Description

values where hard coded as part of #390 and #424
Would be good to move

• train_test_validation_split
• train_validation_test_datetime_split
  to the config model file

Context

Useful not to hard code things

Possible Implementation

in pydantic model file - here and then loaded here

[JackKelly]

oops, sorry, I didn't mean for PR #445 to close this issue!