suppress tagNames parameter form MeasureReader in spark API

[oalam]

the Reader spark component require that the user provide tag names in order to retrieve them from solr. but it could be done automatically through chunk_key field ...

don't forget to udate compactor.yml config file as well

the difficulty is to build the dataframe withe the tag_* columns without knowing the name of that tags. two options :

1. try to extract tags from chunk_key
2. a pre facet query that gives all the tags name