Add "action-outline" / "action-secondary" button type

[aggieN]

What problem does this feature solve?

In the Fipster team, we are currently replacing Vuetify components with Six Webcomponents in our applications. We commonly use the blue outline button, which is not present in the library:

After discussions with our designer, Dimitris Papadopoulos, he suggested that we introduce an additional button for our use case.

What does the proposed API look like?

• introduce new button type "action-outline" or "action-secondary"