feat: Enable expressions as default value in lead/lag function

[sandugood]

Which issue does this PR close?

• Closes Support ColumnExpr in LAG/LEAD for default parameter #22082.

Rationale for this change

In the current DataFusion implementation we can only use a ScalarValue as the default value in both LAG and LEAD window functions. That means that users can't reference other columns' values from the table as default value and create various combinations of them.

It means that currently we cannot perform something like:
lead(col1, 1, col1 / col2) as lead_result

What changes are included in this PR?

1. Added DefaultValue enum that can be either a Literal value or an Expression
2. Reimplemented parse_default_value function to take default_value's type into consideration
3. Added two functions: shift_with_array_default and evaluate_all_with_ignore_null_and_array_default for the situations, when default_value is of DefaultValue::Expression type
4. Added examples for this usecases.

Are these changes tested?

Yes, changes were tested:

1. Added additional unit-tests in the lead_lag.rs.
2. Created separate integration-tests in the /tests subdir.

Are there any user-facing changes?

There are user-facing changes in terms of documentation and DataFusion usage (no syntax changes per se). Also, docs were updated

[comphead]

please have tests in .slt