Implement endpoints to delete emission entries

[redfrexx]

Implement endpoints in the backend to delete data entries. Make sure that the tables with the aggregated emissions data is updated accordingly.

• Delete heating
• Delete electricity
• Delete commuting
• Delete business trip

[codingfabi]

Here are some details about how the endpoints should function:

The endpoints for heating and electricity should function on a working group level and thus be only available for working group representatives.

• One mutation endpoint to delete a heating entry. Only working group representatives should be able to delete the heating entries of their own working group.
• One mutation endpoint to delete a electricity entry. Only working group representatives should be able to delete the electricity entries of their own working group.

The endpoints for commuting and business trip deletion should function in a way that users can only delete their own entries.

This results in 4 separate endpoints.

[codingfabi]

Blocked by #329