feat: add a simplified option for to_graph

[djouallah]

Is your feature request related to a problem?

to_graph is really good but can be very hard to read for a complex transformation

What is the motivation behind your request?

I am just looking for a simple diagram that show relationship between tables and not show the details at the column level

Describe the solution you'd like

something less verbose for a lack of better word compared to the detailed output,

What version of ibis are you running?

9.3

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

duckdb, mssql and spark

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