Introduce new index AllScanIndex, 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, which means a brute force search of the original vector without any encoding

• We also provide an index named all_scan, but you can add configuration items such as quantization and PCA in the configuration parameters of the index

The following is related PRs: