Add max_capacity ENV variable

[dwaard]

The user must be warned if the measured capacity exceeds a maximum given by the government (like 30% of the location's maximum capacity). This warning can be done with the alert message after adding a measurement, like:

• success (green): lower than the maximum allowed capacity
• warning (yellow): around the maximum allowed capacity
• danger (red): larger than the maximum allowed capacity

The colors can also be show in the table below the input field

[dwaard]

The max_capacity (percentage) should be stored somewhere like the .env file