Update soil and litter parameters from `ve_data_science`

[hrlai]

This is a parent issue for @hrlai to keep track of constants / initial values to update from the ve_data_science repo.

The secondary function is to accumulate tasks that belong to the same module / component so we batch update them and reduce the number of unit tests. This applies to constants but not ve_example (see ImperialCollegeLondon/ve_data_science#76 (comment))