Make template `DateTime` show proper tooltip (#28677)
There was a question about "how to improve the datetime display for
SSH/PGP/WebAuthn"
https://github.com/go-gitea/gitea/pull/28262#issuecomment-1831141611
The root problem is that `DateTime` misses the "data-tooltip-content"
attribute, which should be used to make the tooltip popup smoothly.
Now the UI is consistent and the end users could see the detailed
hour/minute/second easily by hovering the element.
