[API] Create a new method to get files directly from repositories df

[ajnavarro]

We need a new method that would get files from repositories using several filters to improve performance.

The first step is to add two new columns to files relation:

• repository_id
• reference_name

Then, we should create a new api method, something like:

def getFiles(repositoriesIds:Seq[String],referenceNames:Seq[String],commitHashes:Seq[String]):DataFrame