chore(egress): symlink /egress to new binary path for backward compatibility

PR #951 moved the egress binary from /egress to /opt/opensandbox-egress/egress
so the supervisor and binary could share a single grouped directory. External
tooling and older deployment manifests may still reference the old /egress
path; add a symlink so both paths resolve to the same binary.

Symlink rather than COPY: zero extra image size, single source of truth for
chmod and replacement, and `exec /egress` resolves to the supervisor-managed
binary like before.

Author: Pangjiping

components/egress/Dockerfile

@@ -131,7 +131,8 @@ COPY --from=builder /out/opensandbox-supervisor /opt/opensandbox-egress/supervis
 COPY components/egress/scripts/cleanup.sh /opt/opensandbox-egress/cleanup.sh
 RUN chmod 0755 /opt/opensandbox-egress/cleanup.sh \
             /opt/opensandbox-egress/egress \
-            /opt/opensandbox-egress/supervisor
+            /opt/opensandbox-egress/supervisor \
+    && ln -s /opt/opensandbox-egress/egress /egress
 
 COPY components/egress/mitmscripts /var/egress/mitmscripts