Make serde errors for unsupported types a bit more actionable

[amoghrajesh]

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Was generative AI tooling used to co-author this PR?

• Yes (please specify the tool below)

Previously these errors said only that a type could not be (de)serialized, giving no indication of what to do about it.
Error looked like

TypeError: cannot serialize object of type <class 'pandas.DataFrame'>

Example in #70791

Name the two ways a Dag author can make their own class work

• a serialize/deserialize method pair
• or @dataclass/@attr.define)

and link to the docs page that already covers all the options in full, instead of leaving people to dig through source to find them.

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[Lee-W]

LGTM