Homogenize monitoring field types

[alfonso-noriega]

Some of the monitoring fields are actually giving a type depending on the original Vind component (i.e. an interval facet for a numeric field will have start and end typed as long/float while a date interval will give back dates). This creates issues when writing the json to an elasticsearch and probably to other non structured DBs.

To solve this identify the fields and translate them to the same type (i.e. dates to timestamp).