mpurins-coralogix

**Describe the bug** When executing following query field in results has integer datatype instead of string. `SELECT cast(c as varchar) FROM (SELECT 1 as c)` **To Reproduce** Pickup this commit...

**Describe the bug** When physical plan includes datafusion builtin function `starts_with` then it is serialized as UDF. **To Reproduce** Following test (can be added in somewhere in https://github.com/apache/arrow-ballista/blob/master/ballista/core/src/serde/physical_plan/mod.rs) should pass...