Add required fields to examples

[vanitabarrett]

Closes #1965

What

• Update component YAML examples to include required attributes for all examples
• The only exception to the above is when we want to intentionally test how a component behaves with invalid data/in certain extremes, e.g: when no data is passed in at all, or when falsey values are provided.

Why

In a previous PR we reviewed the required attributes on all our component options to double check that they're correct (#1979). Following on from that work, we want to make sure the examples in the YAML files (used for tests and to generate macro-options.json and fixtures.json) properly reflect the required attributes.

[36degrees]

The label component also seems to mark the for param as required, but most of the examples do not include it (and the template handles it being omitted) so possibly it shouldn't be marked as required?

[vanitabarrett]

@36degrees Thanks for the review - I think I've addressed them all now in the last few commits. I've marked the label for attribute as not required (49c5308)

[36degrees]

I think this looks good to me. I haven't manually verified every single example - but until we've got a way to programatically validate all the examples I think we have to treat this as a 'best effort' exercise anyway.