Add link to 'Stable' doc version in the Warning Alert on top

As discussed on discord in #documentation channel here

I think this will provide 'further convenience' to website users to upgrade the documentation version by simply clicking on the link in the warning itself as well:

Current Behavior of the Warning Alert on Top:

Proposed change (text can be adjusted accordingly):

Rationale:

• The warning alert already exists, and draws eye attention towards itself (due to its bright color)
• Adding a clickable link is 'further convenience' in terms of UX
• Requires small change in code