React tokens - consume core v6 alphas to enable penta development

[tlabaj]

Core is now publishing 6.0.0-alpha.x pacakges.

React has a v6 branch.

Deliverables for this task:

• consume the core alphas
• make sure the workspace builds
• make sure the global tokens living in https://github.com/patternfly/patternfly/tree/v6/src/patternfly/base/tokens are being turned into react-tokens