Update links to Operate screenshot automation

[akeller]

With the move to the monorepo, there are some broken links in the docs-on-docs:

https://github.com/camunda/camunda-docs/blob/28bc4c96ef1e24132ce7ea0e7cac9984dc95f771/howtos/documentation-guidelines.md?plain=1#L183C1-L189C1

New link - https://github.com/camunda/camunda/tree/main/operate/client/e2e-playwright/docs-screenshots