feat(docs): Add Optional form sections

[stevenj]

Description

Adds Optional Form sections, which enable the Feature of having forms with incomplete sections, which would not pass
validation, but then restricting these to be non optional when the form is finalized.

Description of Changes

Just updates the docs with a new form element type.

Breaking Changes

Nope

Please confirm the following checks

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream module

[github-actions]

✅ Test Report | ${\color{lightgreen}Pass: 374/374}$ | ${\color{red}Fail: 0/374}$ |