add additional property to the coverage identifier api endpoint to provide additional WMS layer names

[ricardogsilva]

This is especially useful for the use case of the datasets that provide an uncertainty visualization, like this:

https://arpav.geobeyond.dev/api/v2/coverages/coverage-identifiers?name_contains=tas_30yr_anomaly_seasonal_agree_model_ensemble-tw2-rcp26-DJF

The idea is that this will allow the frontend to show or hide the uncertainty visualization, which would be achieved by requesting a different WMS layer