replacing the flat index with the IVF family index.

[Thejas-bhat]

No description provided.

Per message from @Thejas-bhat this code'll need a little more work.

[abhinavdangeti]

@Thejas-bhat I'm thinking you should introduce a common helper for the introduce path and merge path where ..

if vectorCount >= 100 {
    indexType = "IVF100,SQ8"
} else if vectorCount >= 10 {
    indexType = "IVF10,Flat"
} else {
    indexType = "IVF1,Flat"
}