fix(snmp): migrate seed snmp.yml to auths/modules schema for v0.30.1 compatibility

The init-container seeds /etc/snmp_exporter/snmp.yml from this ConfigMap
before the snmpexporter container starts. The previous seed used the
pre-v0.24 flat schema (module names at top level) which snmp_exporter
v0.30.1 rejects at startup, causing CrashLoopBackOff and helm install
to time out with context deadline exceeded.

Replace with a minimal valid stub in the auths/modules split schema.
The Day-1 generate_snmp primitive overwrites this with the real config.