Support 'name' attribute (if set) in webform mapping

[bgilhome-now]

PR for feature request #1410

Issue:

What I did

• Use 'name' attribute if set in webform element config as the field key/name, else use machine_name as usual.

How to test

• Build a webform, and for an element, add a custom 'name' attribute in the element's config
• View the form in the frontend and confirm the HTML 'name' attribute uses the custom value

Checklist

For all PR's

• I've added relevant changes to the project Readme if needed
• I've updated the documentation site as needed
• I have added tests to cover my changes (if not applicable, please state why in a comment)

For new UI components only

• I have added a storybook story covering all variants
• I have checked a11y tab in storybook passes
• I have added cypress component tests (if the component is interactive)
• Any events are emitted on the event bus using emitRplEvent