FIO-8461: Fixes checkbox with radio input type not present in submission on 5.x renderer

[mikekotikov]

Link to Jira Ticket

https://formio.atlassian.net/browse/FIO-8461

Description

What changed?

Previously, Checkbox with input type 'radio' and key + value set wasn't present in submission if left empty. This PR fixes this behavior by making specified key be present in submission.

Why have you chosen this solution?

I've made it to work same way as if you check -> uncheck the checkbox. In this case it was set to the submission object with empty string value ("").

Dependencies

None

How has this PR been tested?

I added automated test to cover the buggy case

Checklist:

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation (if applicable)
• My changes generate no new warnings
• My changes include tests that prove my fix is effective (or that my feature works as intended)
• New and existing unit/integration tests pass locally with my changes
• Any dependent changes have corresponding PRs that are listed above