Introduce new index BruteForce, means scan all point in base

[LHT129]

We don't have an index similar to brute force search yet. Further, we can abstract this type of index into a full scan index, which supports certain quantization encoding or compression such as PCA, but the core feature is that each point in the candidate set will participate in each query.

• We provide a special index named brute_force external, if pass no argument, it means a brute force search of the original vector without any encoding. you can also add configuration items such as quantization and PCA in the configuration parameters of the index

The following is related PRs:
#299