feat: add Input with support for type='checkbox'

[kurtdoherty]

Context

• We're delivering new core table components and we require a checkbox component to enable row selection.
• The existing Checkbox component includes a lot of functionality that is simply irrelevant to row selection (such as visual labels and supplementary information).
• Ideally, we want a thin wrapper around an <input type="checkbox"> so that we have the correct checkbox visual appearance, without any of the additional label handling. That way, this low-level input component can be used internally by Checkbox and our row selection table component.

This PR

• Adds a new Input component with support for type="checkbox". This component will be expanded to support other input types and represents the lowest-level styled input component in Elements.

[rpt-uk-github]

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[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
Report missing for 885de7a1	✅ 100.00%

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (885de7a)	Report Missing	Report Missing	Report Missing
Head commit (5c84210)	8660	8021	92.62%

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#737)	24	24	100.00%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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