feat: `nulls first` / `nulls last` in `array_sort`

[MarcoGorelli]

Is your feature request related to a problem?

array_sort is missing options to control nulls first / last, like DuckDB and Polars have

What is the motivation behind your request?

control null placement

Describe the solution you'd like

.sort(nulls_first=True)

What version of ibis are you running?

11

What backend(s) are you using, if any?

duckdb

Code of Conduct

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