nice and unique units in pyaerocom output for aeroval

[heikoklein]

Is your feature request related to a problem? Please describe.
The maps endpoint/json files and the ts endpoint/json-files contain units of observations and models. Even if they are run from the same config the units of these endpoints can be slightly different, e.g. https://aeroval.met.no/pages/maps/?project=emep&experiment=2024-reporting and https://aeroval.met.no/pages/evaluation/?project=emep&experiment=2024-reporting show the same but differently notated units, e.g. ug N m-3
vs µg N / m3.

This is both confusing for end-users and for also for data-checks like: https://github.com/metno/AeroToolsIssues/issues/62

The units should be written using the same notation from the configuration. The units should be both CF-compliant and nice. udunits as basis of the CF-Convention allows nowadays superscripts and µ, e.g. µg N / m³ is nice and accepted

Describe the solution you would like to see

Units of a component should come from one configuration and support µ and ³.