Enhance Frontend validation and UX when adding or editing Charts

[nicolaes]

Is your feature request related to a problem? Please describe.
Configuring the columns for a new chart can end up in long trial and error sequences if you're not familiar with the data, the data types and the chart types.

Describe the solution you'd like

1. X data column is required
2. Replace the empty option in Y data column with "Row count"
   Currently, leaving an empty value defaults to COUNT(*), which is the same regardless of selected Y column
3. Disable Y function dropdown if "Row count" is selected in Y data
4. Remove "Count" from Y function dropdown
5. Remove "Temporal data" field if it's not used

Describe alternatives you've considered
I did not think about other implementations.

Additional context

[nicolaes]

Implementing 1st requirement fixes server errors when viewing a broken chart.