💡Reduce constant minimum Tunnel connection bandwidth (follow-on issue)

**Describe the feature you'd like**
This is specific followup request from issue which was closed: "Significantly reduce basic Tunnel bandwidth for cell modem #935"
That response partially resolved the core issue (see below).
We use cell modems at some customer sites to our AI-based BMS (building management system), running Windows, controlling tens of IoT control devices. We need to minimize expensive cell modem bandwidth.
We still need each CONNECTION to consume less bandwidth. See attached screenshots, which prove each connection uses 0.8-1.1MB/hour simply to maintain itself, not counting application data exchanged. We accept lower reliability and slow reconnection of a lost connection. We would expect the solution to be sending metrics & keep-alive packets much less frequently.

**Describe alternatives you've considered**
--metrics-update-freq 30 (default is 5) -- in early testing, we didn't see any improvement
--ha-connections 1 -- per above-referenced issue #935, that DID reduce number of connections from 4 to 1, which did indeed reduce bandwidth 75%. Thank you!

**Additional context**
Screenshot of cell modem traffic in MB attached. Hour periods with under 0.25MB are no Tunnel running. Those near/above 1MB are with Tunnel running, with only ONE connection (--ha-connections 1). That one connection typically consumes 1.1MB (Tunnel running)-0.25MB(Tunnel not running)=0.85MB/hour. Ignore larger MB hours - that is application or Windows traffic.