Update confluentinc/cp-kafka docker tag to v7

Editor assessment

Updating the confluentinc/cp-kafka docker tag to v7 names the image and the major tag jump plainly, so the reader knows exactly which container pin moved. The chore(deps) type and scope fit this infrastructure maintenance change. A major tag bump can hide compatibility risk, and a body noting tested behavior would have added value, but the metadata marks nothing breaking and the subject is unambiguous. No body or footers appear. Hygiene is clean: imperative mood, no trailing period, precise subject, no pasted content. Clear, sufficient maintenance communication.