feat: add required as modifiable property

[soleksy-splunk]

Issue number: https://splunk.atlassian.net/browse/ADDON-73241

Summary

Possibility to modify require parameter on front-end

Changes

fieldsToModify also supports require property. (only front-end part)

User experience

User right now can modify also required property in other form fields.

Checklist

If your change doesn't seem to apply, please leave them unchecked.

• [x] I have performed a self-review of this change
• [x] Changes have been tested
• [x] Changes are documented
• [x] PR title follows conventional commit semantics

[vtsvetkov-splunk]

should we add the example into the kitchen sink globalConfig.json? Just to be sure we think we changed the schema.json right

[soleksy-splunk]

should we add the example into the kitchen sink globalConfig.json? Just to be sure we think we changed the schema.json right

yea, maybe worth adding it. Will do it