feat(query): add l2 distance operator <->

[sundy-li]

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Summary

Summary about this PR

1. add l2 distance operator <->, pgvector has this operator, let's have it in databend

2. remove unused codes

• Closes #issue

MySQL [(none)]> select  [1, 2] <-> [2, 3];;
+---------------------+
| ([1, 2] <-> [2, 3]) |
+---------------------+
|           1.4142135 |
+---------------------+
1 row in set (0.015 sec)

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[BohuTANG]

This is ready for document, cc @soyeric128