Correct sensors

[Flix6x]

This PR updates some units and resolutions of sensors. I guess this is a good opportunity to discuss how we should handle database migrations coming from plugins. Just a proposal: add a CLI command in the plugin, one for each migration?

[nhoening]

Here is one direction to think towards: Each plugin can use its own alembic migrations. The plugin could configure that its table is {plugin_name}_alembic_version, so its history of migrations is not mixed with the one from FlexMeasures. Of course, one needs to be careful with changes. If the plugin authors remove a column FlexMeasures works with, for example, things will break. But right now it seems doable. That would be one step more for plugins to be full projects on their own.

[Flix6x]

Worthwhile to note: this PR also moves from an hourly to a quarterhourly CO₂ signal.

Migration steps for correcting units and resolutions:

update sensor set (unit, event_resolution) = ('MW', interval '15 minutes') where (name='Scheduled generation' and unit='MWh' and event_resolution=interval '1 hour');
update sensor set unit='MW' where (name='Solar' and unit='MWh');
update sensor set unit='MW' where (name='Onshore wind' and unit='MWh');
update sensor set unit='MW' where (name='Offshore wind' and unit='MWh');
update sensor set event_resolution=interval '15 minutes' where (name='CO2 intensity' and unit='kg/MWh' and event_resolution=interval '1 hour');

Migration steps for correcting names:

update sensor set name='Wind Onshore' where (name='Onshore wind');
update sensor set name='Wind Offshore' where (name='Offshore wind');
update sensor set name='CO₂ intensity' where (name='CO2 intensity');

Finally, rerun flexmeasures entsoe import-day-ahead-generation --from-date <however far your history went> to fill in the missing quarterhourly values.