[Discussion] Define python UDF using `CREATE FUNCTION` SQL statement

**Is your feature request related to a problem or challenge? Please describe what you are trying to do.**

I would like to be able to define a python function using SQL `CREATE FUNCTION` statement.

Something like

```rust
let sql = r#"
CREATE FUNCTION to_miles(DOUBLE)
RETURNS DOUBLE
LANGUAGE PYARROW
AS '
import pyarrow.compute as pc

conversation_rate_multiplier = 0.62137119

def to_miles(km_data):
return pc.multiply(km_data, conversation_rate_multiplier)
'
"#;

ctx.sql(sql).await?.show().await?;

ctx.sql("select double_col, to_miles(double_col) from t")
.await?
.show()
.await?;
```

**Describe the solution you'd like**

datafusion provides pluggable `datafusion::execution::context::FunctionFactory` which could be wired to interpret python function definitions.

we could provide column based function definitions (`LANGUAGE PYARROW`) or row based (`LANGUAGE PYTHON`)

**Describe alternatives you've considered**

**Additional context**

- databricks has [similar functionality](https://docs.databricks.com/aws/en/udf/unity-catalog)

Start at datafusion::execution::context::FunctionFactory and trace how SQL CREATE FUNCTION definitions could be connected to Python UDF execution. Clarify whether column-based LANGUAGE PYARROW and row-based LANGUAGE PYTHON are in scope, then validate the CREATE FUNCTION and SELECT flow shown in the issue.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.