feat: add Vector Index API

PiperOrigin-RevId: 618867415

google/firestore/admin/v1/index.proto

@@ -16,6 +16,7 @@ syntax = "proto3";
 
 package google.firestore.admin.v1;
 
+import "google/api/field_behavior.proto";
 import "google/api/resource.proto";
 
 option csharp_namespace = "Google.Cloud.Firestore.Admin.V1";
@@ -92,6 +93,25 @@ message Index {
       CONTAINS = 1;
     }
 
+    // The index configuration to support vector search operations
+    message VectorConfig {
+      // An index that stores vectors in a flat data structure, and supports
+      // exhaustive search.
+      message FlatIndex {}
+
+      // Required. The vector dimension this configuration applies to.
+      //
+      // The resulting index will only include vectors of this dimension, and
+      // can be used for vector search with the same dimension.
+      int32 dimension = 1 [(google.api.field_behavior) = REQUIRED];
+
+      // The type of index used.
+      oneof type {
+        // Indicates the vector index is a flat index.
+        FlatIndex flat = 2;
+      }
+    }
+
     // Can be __name__.
     // For single field indexes, this must match the name of the field or may
     // be omitted.
@@ -105,6 +125,10 @@ message Index {
 
       // Indicates that this field supports operations on `array_value`s.
       ArrayConfig array_config = 3;
+
+      // Indicates that this field supports nearest neighbors and distance
+      // operations on vector.
+      VectorConfig vector_config = 4;
     }
   }