feat: add a `to_json()` output method

[lostmygithubaccount]

Is your feature request related to a problem?

in writing documentation/demos, I would like a to_json() method on tables for consistency with the other read_* and to_* methods

I'm not sure how JSON vs JSONL should be handled

Describe the solution you'd like

[ins] In [1]: import ibis
ibi
[nav] In [2]: t = ibis.examples.penguins.fetch()
i
[ins] In [3]: t.to_json("penguins.json")

What version of ibis are you running?

main

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

DuckDB mainly, but this should apply to any backend that supports JSON output

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