Method add_to_existing implemented

[havent-invented]

Retrieval with functionality of adding new documents implemented. Method add_to_existing implemented in RetrievalAugmentation

[jalotra]

@havent-invented
The update would not be that simple, the tree building phase does this :

1. Starts with leaf nodes. 
2. Creates summarisations on top of those leaf nodes and do this recursively upwards.
3. Stops at some layer `L` which it > 0, 0 being the leaf nodes layer.

Now let's see what would happen in merge operation, say merge(Tree A, Tree B)

1. The summarisation op would have to be done again.
2. Because the tree creation is inherently pivoted on combining some `Nodes : N` based on max of some metric using UMAP.

[jytheawesome]

Hey, @parthsarthi03, the add_to_existing feature would be insanely useful for my use case (adding documents to an existing RAG tree). I see that this branch is implementing this feature and that @ET-yzk has already approved it. Not sure if it is ready to be merged :)

Thanks in advance!