Docs: consistency between custom buttons, popovers and tooltips

[julien-deramond]

Description

This PR updates _component-examples.scss for .custom-tooltip and .custom-popover.

Custom tooltip background color is set to violet and the color is forced to white to avoid contrast issues (in the actual main branch, on dark mode, the text color is not accessible).

Custom popover background and border colors are set to violet.

Motivation & Context

IMO this change can enhance the comprehension of our custom examples in the documentation by using a color absent from our default theme colors. It enforces the consistency with the custom buttons in https://twbs-bootstrap.netlify.app/docs/5.3/components/buttons/#variables which is better, still IMO, compared to the corresponding popovers and tooltips examples.

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
• (N/A) I have added tests to cover my changes
• All new and existing tests passed

Live previews

• Reference: https://deploy-preview-38681--twbs-bootstrap.netlify.app/docs/5.3/components/buttons/#variables
• https://deploy-preview-38681--twbs-bootstrap.netlify.app/docs/5.3/components/tooltips/#custom-tooltips
• https://deploy-preview-38681--twbs-bootstrap.netlify.app/docs/5.3/components/popovers/#custom-popovers