debt: be more stringent in validating data sent to soilDataPush mutation

[shrouxm]

Currently if the user sends duplicate entries to the soilDataPush mutation we just apply the entries. Ideally clients should only specify entities once, to make intent unambiguous, and not doing so could be a smell that there's a client bug on the loose, so we should reject such requests. As it stands that could mean:

• sending duplicate sites
• sending duplicate depth dependent data entries
• sending duplicate depth intervals for update or deletion