Use variable as default indexName for ES mapping features

A common use case for customers is to use the same ES server with different index names for different environments

=> The default index name for ES mapping features in Studio should be ${elasticsearch.indexName:=nuxeo} instead of just nuxeo.

=> The generated json file should be prefixed with project id+ index counter.

=> A tooltip should be added next to the Index Name field on the editor to explain the default variable and that other variables can be used if needed