fr(stepper): add a way to better handle steps with long titles

#### Bug, feature request, or proposal:

Request/Proposal: Add the ability to use a tooltip for Step-Headers.

#### What is the expected behavior?

Having an text input for a tooltip or a template html input for tooltip like with the step-label.

#### What is the current behavior?

None

#### What is the use-case or motivation for changing an existing behavior?

This is useful if you want to have a long step (optional-)label in (mostly horizontal-)steppers or just want to add additional information for the step without touching the design.

Start by reading the stepper and step-label APIs, especially how the existing step-label template supports additional content. Determine how a text input or HTML template could provide tooltip content for step headers, then verify that long or optional labels can expose the tooltip without changing the stepper design.

Written by the indexing model from the issue text.