fix: Rename webhooks plugin to `wpgraphql-webhooks`

The wp-graphql-webhooks plugin should be renamed to wpgraphql-webhooks in order to align with the new naming standard.

<img width="698" height="276" alt="Image" src="https://github.com/user-attachments/assets/b077680b-54e7-400b-8b72-27be48ca0ca0" />


<img width="2594" height="1252" alt="Image" src="https://github.com/user-attachments/assets/c56bad3e-2382-4754-8cd2-cffe53a4f25e" />