Add the support for IndexIDMap with Cagra index (#4188)

Summary:
## Description
Add the support for adding vectors with ids when IndexIDMap is used with Cagra Index.

Resolves issue: #4107

Pull Request resolved: #4188

Reviewed By: mnorris11

Differential Revision: D69812544

Pulled By: gtwang01

fbshipit-source-id: 3c12c930e5d10ce214b12e68dacd63a644011b79

Author: navneet1v

faiss/gpu/GpuIndexCagra.cu

@@ -103,6 +103,10 @@ void GpuIndexCagra::train(idx_t n, const float* x) {
     this->ntotal = n;
 }
 
+void GpuIndexCagra::add(idx_t n, const float* x) {
+    train(n, x);
+}
+
 bool GpuIndexCagra::addImplRequiresIDs_() const {
     return false;
 };

faiss/gpu/GpuIndexCagra.h

@@ -245,6 +245,12 @@ struct GpuIndexCagra : public GpuIndex {
             faiss::MetricType metric = faiss::METRIC_L2,
             GpuIndexCagraConfig config = GpuIndexCagraConfig());
 
+    /// Trains CAGRA based on the given vector data and add them along with ids.
+    /// NB: The use of the add function here is to build the CAGRA graph on
+    /// the base dataset. Use this function when you want to add vectors with
+    /// ids. Ref: https://github.com/facebookresearch/faiss/issues/4107
+    void add(idx_t n, const float* x) override;
+
     /// Trains CAGRA based on the given vector data.
     /// NB: The use of the train function here is to build the CAGRA graph on
     /// the base dataset and is currently the only function to add the full set