feat: support Union

[KKould]

What problem does this PR solve?

select 1 union select 3 union select 2

+---+
| 1 |
+===+
| 3 |
|---|
| 1 |
|---|
| 2 |
+---+

explain select 1 union select 3 union select 2

+--------------------------------------------------+
| PLAN                                             |
+==================================================+
| Aggregate [] -> Group By [1] [HashAggregate]     |
|   Union left: [1], right: [2]                    |
|     Aggregate [] -> Group By [1] [HashAggregate] |
|       Union left: [1], right: [3]                |
|         Projection [1] [Project]                 |
|           Dummy [Dummy]                          |
|         Projection [3] [Project]                 |
|           Dummy [Dummy]                          |
|     Projection [2] [Project]                     |
|       Dummy [Dummy]                              |
+--------------------------------------------------+

Code changes

• Has Rust code change
• Has CI related scripts change

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Note for reviewer