Add CORS support for GWAS

[haideriqbal]

Request details:

For context, we have been developing an online validator for one of our type of data files which contains EFO terms we need to validate using the OLS REST api (example of request: https://www.ebi.ac.uk/ols4/api/ontologies/efo/terms?obo_id=EFO:0001645). It works perfectly when using the validator on a local computer, but from a server, the request gets rejected with a CORS error:

```https://www.ebi.ac.uk/ols/api/ontologies/efo/terms?obo_id=EFO:0001645' from origin '[https://pgscatalog.org](https://validate-dot-pgs-catalog.appspot.com/)' has been blocked by CORS policy: No 'Access-Control-Allow-Origin' header is present on the requested resource.