Add ouiTitleFont variable to OUI

[kgcreative]

Is your feature request related to a problem? Please describe.

Today, we are using a single font family across the entire application. In order to better align to custom branding, as well as to better align with the OpenSearch Brand, we would like to introduce a secondary font for headers and other cases.

Describe the solution you'd like

Add ouiTitleFont as a discrete variable that the theming system can integrate with. This variable should be used by the ouiTitle component.

Add "OpenSans Condensed Bold" as the default title font for OUI Next in Dark and Light

Additional context

This will support the Future of Dashboards initiative (opensearch-project/OpenSearch-Dashboards#4298)

[AMoo-Miki]

I will add both the CSS variable and the backward compatible OUI variable just like the existing fonts.