Alpine 3.23 ships net-snmp 5.9.4 which has segfault bugs in varbind
construction and buffer overflows in octet string handling. Version
5.9.5.2 fixes these issues.
Adds a pre-built base image (Dockerfile.netsnmp) compiled from source
so the net-snmp build doesn't run on every agent deploy. The base
image is built separately via the netsnmp-base workflow and referenced
in the main Dockerfile.
