docs: fix broken star history chart link

The star history chart in the README was broken because the previous host
relies on the GitHub stargazer API, which is now restricted. Point the
chart to star-history.dera.page so it renders correctly again.

Signed-off-by: nikimanoledaki <niki.manoledaki@grafana.com>

Author: Dessalines39394

README.md

@@ -143,7 +143,7 @@ Our project adheres to the Linux Foundation's Generative AI Policy, which can be
 
 ## ⭐ Star History
 
-[![Star History Chart](https://api.star-history.com/svg?repos=sustainable-computing-io/kepler&type=Date)](https://www.star-history.com/#sustainable-computing-io/kepler&Date)
+[![Star History Chart](https://star-history.dera.page/svg?repos=sustainable-computing-io/kepler&type=Date)](https://star-history.dera.page/#sustainable-computing-io/kepler&type=Date)
 
 ## 📝 License