Update masthead to HeroDevs EOL

[edezekiel]

Description

Updated homepage of getbootstrap.com , add yellow banner on the top of the page with link to HeroDevs.

Motivation & Context

Introduces Never-Ending Support for Bootstrap.

Type of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would change existing functionality)

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
• I have added tests to cover my changes
• All new and existing tests passed

Live previews

• https://deploy-preview-39749--twbs-bootstrap.netlify.app/

Related issues

[jwcalles]

@mdo here is the adjustment to the homepage that we discussed. Adding the masthead/banner pointing potential Bootstrap v3 and v4 users to the extended long-term support offering.

@edezekiel on our team put the PR together for your review, happy to make any required changes or edits.

[aavorthmann]

@mdo is there anything I can help with on this one? Do I need to request a specific reviewer ?

[mdo]

Manually added to gh-pages in #39787. This PR ensures we'll have it in our next release as well.