Optimize index type for using

[nameczz]

Describe the feature:

IndexType in Milvus.ts file is useless for now. Should we define an indexType for the convenience of users?

Describe a specific use case for the feature:
Then we can code like:
await milvusClient.createIndex({
collection_name: COLLECTION_NAME,
field_name: VECTOR_FIELD_NAME,
extra_params: {
index_type: IndexType.BIN_IVF_FLAT,
metric_type: 'TANIMOTO',
params: JSON.stringify({ nlist: 1024 }),
},
});