Add builder constructor that takes algo params

src/main/java/com/amazon/opendistroforelasticsearch/knn/index/KNNVectorFieldMapper.java

@@ -101,10 +101,21 @@ public static class Builder extends ParametrizedFieldMapper.Builder {
                 }, m -> toType(m).dimension);
         private final Parameter<Map<String, String>> meta = Parameter.metaParam();
 
+        private String spaceType;
+        private String m;
+        private String efConstruction;
+
         public Builder(String name) {
             super(name);
         }
 
+        public Builder(String name, String spaceType, String m, String efConstruction) {
+            super(name);
+            this.spaceType = spaceType;
+            this.m = m;
+            this.efConstruction = efConstruction;
+        }
+
         @Override
         protected List<Parameter<?>> getParameters() {
             return Arrays.asList(stored, hasDocValues, dimension, meta);
@@ -122,10 +133,21 @@ protected Explicit<Boolean> ignoreMalformed(BuilderContext context) {
 
         @Override
         public KNNVectorFieldMapper build(BuilderContext context) {
+            if (this.spaceType == null) {
+                this.spaceType = getSpaceType(context.indexSettings());
+            }
+
+            if (this.m == null) {
+                this.m = getM(context.indexSettings());
+            }
+
+            if (this.efConstruction == null) {
+                this.efConstruction = getEfConstruction(context.indexSettings());
+            }
+
             return new KNNVectorFieldMapper(name, new KNNVectorFieldType(buildFullName(context), meta.getValue(),
                     dimension.getValue()), multiFieldsBuilder.build(this, context),
-                    ignoreMalformed(context), getSpaceType(context.indexSettings()), getM(context.indexSettings()),
-                    getEfConstruction(context.indexSettings()), copyTo.build(), this);
+                    ignoreMalformed(context), this.spaceType, this.m, this.efConstruction, copyTo.build(), this);
         }
 
         private String getSpaceType(Settings indexSettings) {
@@ -346,7 +368,7 @@ protected boolean docValuesByDefault() {
 
     @Override
     public ParametrizedFieldMapper.Builder getMergeBuilder() {
-        return new KNNVectorFieldMapper.Builder(simpleName()).init(this);
+        return new KNNVectorFieldMapper.Builder(simpleName(), this.spaceType, this.m, this.efConstruction).init(this);
     }
 
     @Override