Fix Form elements and field set spacing

Problem/Motivation

Reported by Alaa Jwiehan

Forms and Webforms have no vertical spacing between elements.

Proposed resolution

Add more spacing between for form fieldsets (about 20px of bottom margin looks nice)

Using the mb-3 fallback by Bootstrap Barrio.

Remaining tasks

• ✅ File an issue about this project
• ✅ Addition/Change/Update/Fix to this project
• ✅ Testing to ensure no regression
• ➖ Automated unit/functional testing coverage
• ➖ Developer Documentation support on feature change/addition
• ➖ User Guide Documentation support on feature change/addition
• ➖ Update Release Notes and Update Helper on new feature change/addition
• ✅ Code review from 1 Varbase core team member
• ✅ Full testing and approval
• ✅ Credit contributors
• ✅ Review with the product owner
• ❌ Release varbase-9.1.0-beta1, vartheme_bs5-1.0.0-beta1

Varbase update type:

• ✅ No Update
• ➖ Optional Update
• ➖ Forced Update
• ➖ Forced Update if Unchanged

User interface changes

• N/A

API changes

• N/A

Data model changes

• N/A