Change the hardcoded URL for the GSA REST API in Bulk Expression Atlas

[ke4]

For gene set enrichment we are using an external API that is down.
It is a REST service that should be run by our group, but it is currently not up and running.
The API is defined in this line: GSA_URL_PATTERN : https://www.ebi.ac.uk/fg/gsa/api/tsv/getOverlappingComparisons/{0}/{1}
where

0: name of the species
1: bioentity identifiers separated by spaces

We need to change this hardcoded URL to reflect the environment that they are deployed to. So, if it is staging for example then it should call the GSA API in this URL: https://wwwdev.ebi.ac.uk/fg/gsa/api/tsv/getOverlappingComparisons/{0}/{1}

[ke4]

We should postpone all the gene set enrichment tickets for now and wait for the new GTL to make a decision regarding them.
We need to decide if we need to restore this service or remove it completely.