Throw an error if two covariate builders generate overlapping covariate IDs

[schuemie]

When calling getDbCovariateData() with a list of covariate settings, FeatureExtraction iterates over the builders, and appends the covariate data. It would be good if an error was thrown if two covariate builders create overlapping covariate IDs.

For speed it may be advisable to check overlap based on covariateRef rather than covariates itself.