docs(examples): add usage examples for get_backend and get_name

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Description of changes

Adds examples by creating a table using an in-memory duckdb connection for get_backend and get_name.

I did backend.name to get "duckdb" in the example for get_backend rather than backend to avoid getting something like "<ibis.backends.duckdb.Backend at 0x7fffd919b470>". I'm not sure if both that and the type usage are necessary; maybe we could use one or the other if we don't want to use both.

[cpcloud]

You can use # doctest: +ELLIPSIS (note the two spaces preceding the #) when dealing with values that can vary between invocations of Python:

>>> class Foo: pass  # doctest: +ELLIPSIS
>>> Foo()
<__main__.Foo at ...>

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You can use # doctest: +ELLIPSIS (note the two spaces preceding the #) when dealing with values that can vary between invocations of Python:

>>> class Foo: pass  # doctest: +ELLIPSIS
>>> Foo()
<__main__.Foo at ...>

This is super useful; thank you for sharing that trick! I will keep this in mind for future scenarios where it might be cleaner to show the instance of the class itself.