Change watering amounts of own waterings

[joergreichert]

state of the art: once made watering entry cannot be edited

motivation: Made a mistake when entering the watered amount and want to correct it afterwards

future state:

• Can edit own watering entry and change the amount of liters (via inline edit), see also #6 (for common used editing infrastructure)
• changed liters are persisted via API call in database

[joergreichert]

Update watering: https://user-images.githubusercontent.com/994131/162630507-381b5f77-b87a-42c8-968d-571afbe99d45.mp4

[joergreichert]

DONE: https://github.com/CodeforLeipzig/leipziggiesst/commit/2f056415773f53ba03d30e2269f402160640d10d