Change outdated Bootstrap 4 documentation texts and links on the 5.5.x branch

Problem/Motivation

Having text and links which are outdated and for Bootstrap 4 in the 5.5.x branch for Bootstrap 5

Steps to reproduce

Given that the Bootstrap Barrio 5.5.x was installed
When I go to "/admin/appearance/settings/bootstrap_barrio"
And click on the "Components" vertical tab
And open the "Buttons" detail item
Then the following description for the setting field "Use .btn-default-outline class. See Outline buttons in the Bootstrap 4 documentation."

Proposed resolution

• Change all Bootstrap 4 outdated text to Bootstrap 5
• Change all Bootstrap 4 links to the new documentation or code links
• Change to use "https://cdn.jsdelivr.net/npm/bootswatch@5.0.1/dist" for bootswatch

Remaining tasks

• Change
• Test
• Automated test
• Review
• Release

User interface changes

All text and links will be around Bootstrap 5

API changes

• None

Data model changes

• None