feat: proxy / bridgeservicefinder: Add config flag to control automatic registration of newly discovered networks in bridgeservicefinder

[joanestebanr]

Feature Request

bridgeservicefinder, used by aggkit-proxy, automatically discovers new networks as soon as they are added to AggLayer, and immediately starts using them.
This causes two related problems:

1. Incomplete network data: a network can be registered in AggLayer before it has a bridgeURL or the required RPC endpoint configured. When bridgeservicefinder picks it up anyway, aggkit-proxy ends up trying to operate against a network that isn't actually ready to be used.
2. dev-ui can't keep up dynamically: dev-ui currently has no mechanism to dynamically pick up newly added networks. As a result, when bridgeservicefinder starts using a network automatically, the overall system ends up in an inconsistent/confusing state — the backend treats the network as active while the UI has no awareness of it.

Proposal

Introduce a configuration parameter that controls whether newly discovered networks are automatically added and put into use by bridgeservicefinder, or whether they require an explicit/manual step before being enabled.

• When automatic registration is enabled (current behavior): networks are discovered and used as soon as they appear in AggLayer, as today.
• When automatic registration is disabled: newly discovered networks are detected but not activated automatically; activation would require [manual approval / a separate trigger — TBD], avoiding the issue of half-configured networks being used prematurely, and giving time for dev-ui support (or other dependent systems) to catch up.