operator: Use absolute path in Dockerfile ENTRYPOINT

The distroless base image has no $PATH, so the relative command
"redpanda-operator" cannot be resolved. Normally the Helm chart
overrides the entrypoint via the pod spec command field, but when
the command is cleared (e.g. for dlv debugging) the container falls
back to the Dockerfile ENTRYPOINT and fails with "executable file
not found in $PATH".

Use the absolute path "/redpanda-operator" to match where the binary
is installed (line 11).

Author: RafalKorepta

operator/Dockerfile

@@ -15,4 +15,4 @@ COPY redpanda-operator-${TARGETOS}-${TARGETARCH} /redpanda-operator
 # that still specify old entrypoints/commands.
 COPY alias-${TARGETOS}-${TARGETARCH} /manager
 
-ENTRYPOINT ["redpanda-operator", "run"]
+ENTRYPOINT ["/redpanda-operator", "run"]