What problem does this PR solve?

Support for POSITION() Function. POSITION(pattern in s USING CHARACTERS/OCTETS) is not implemented since it's not supported by sqlparser

Issue link: #130

What is changed and how it works?

=> SELECT POSITION('bc' in 'abcd');
 position(bc in abcd)
----------------------
                    2
(1 row)

=> SELECT POSITION('de' in 'abcd');
 position(de in abcd)
----------------------
                    0
(1 row)

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