[yaml] Fix examples catalog tests

[Polber]

This PR fixes a few tests in the YAML examples catalog, including enabling the Spanner tests which were previously excluded.

There are a couple of organizational changes including separating error_handling into a separate file. This was to allow LogForTesting to use the error_handling framework which is handy for examples tests that replace WriteTo transforms with LogForTesting ad-hoc that consume an error output of an upstream WriteTo transform.

This is also a prereq to #32289

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[Polber]

R: @robertwb

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[robertwb]

Thanks.

[robertwb]

Do we expect this to every have errors (that we'd want to ignore)?

[Polber]

The only case for Python I can think of is if it is somehow not JSON parseable (Possibly a custom provider upstream that does not return Row)

For Java, I could see there being other issues (for starters, doesn't ERROR throw and exception when it logs?)

Regardless, this change was mostly for making it easier to hot-swap LogForTesting in example pipelines that define error_handling Write transforms. But I could also create a custom Log transform within the examples test file if you think that makes more sense?

[robertwb]

Sure, that's fine.

[robertwb]

Looks like this needs a rebase.