### What problem does this PR solve?

Add license statement.

### Type of change

- [x] Refactoring

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

### What problem does this PR solve?

Update displayed_name to display_name

### Type of change

- [x] Refactoring

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

Fix test cases

### Type of change

- [x] Other (please describe): Fix error cases

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Signed-off-by: jinhai <haijin.chn@gmail.com>

### What problem does this PR solve?

Add tests for frontend API

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

Added doc for switching elasticsearch to infinity

### Type of change

- [x] New Feature (non-breaking change which adds functionality)
- [x] Documentation Update

### What problem does this PR solve?

Integration with Infinity

- Replaced ELASTICSEARCH with dataStoreConn
- Renamed deleteByQuery with delete
- Renamed bulk to upsertBulk
- getHighlight, getAggregation
- Fix KGSearch.search
- Moved Dealer.sql_retrieval to es_conn.py


### Type of change

- [x] Refactoring

### What problem does this PR solve?

fix bugs in test

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

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Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

### What problem does this PR solve?

Add test for API

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

---------

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>
Co-authored-by: Zhichang Yu <yuzhichang@gmail.com>