Docs: add margin between buttons in tooltip examples

[julien-deramond]

Description

This PR suggests to add some margin around the buttons used in Docs > Tooltips > Directions example. The values used are the same as the one used in the standard buttons example:

> .btn,
> .btn-group {
  margin: .25rem .125rem;
}

The Cheatsheet example is not impacted by this change because it has its own margin rules:

[id="tooltips"] .bd-example .btn {
  margin: 0 1rem 1rem 0;
}

Motivation & Context

This change adds some space around the buttons when the screen width is reduced to avoid:

Type of changes

• Enhancement (non-breaking change)

Checklist

• I have read the contributing guidelines
• My code follows the code style of the project (using npm run lint)
• My change introduces changes to the documentation
• I have updated the documentation accordingly
• All new and existing tests passed

Live previews

• https://deploy-preview-37492--twbs-bootstrap.netlify.app/docs/5.2/components/tooltips/
• https://deploy-preview-37492--twbs-bootstrap.netlify.app/docs/5.2/examples/cheatsheet/#tooltips (for non-regression testing)

Related issues

N/A