ICMP-based discovery with manual parent-child device linking

Is your feature request related to a problem? Please describe. OneUptime currently supports SNMP-based Discovery Scans to find devices and build Network Topology links. However, many devices on our network don't support/respond to SNMP and can only be discovered via ICMP (ping). There's currently no ICMP-based discovery scan type, so these devices aren't discovered automatically. Additionally, when automatic topology link discovery fails (no SNMP/LLDP/CDP data to determine relationships), there's no way to manually define how a discovered device fits into the topology.

Describe the solution you'd like

• Add an ICMP Discovery Scan type, alongside the existing SNMP Discovery Scan, to find devices that only respond to ping.
• Add a manual "Link Device" option in Network Topology / Devices, so that when auto-discovery can't determine the parent-child relationship, a user can manually assign one device as the parent of another (e.g., Router → parent; Switch → child of Router; Access Point → child of Switch, i.e. grandchild of Router).
• Allow ICMP-discovered devices to be manually linked as children under existing SNMP-discovered devices (e.g., linking an ICMP-only device as a child of the Switch it's physically connected to), so the full topology tree is complete even where auto-discovery has gaps.

Describe alternatives you've considered Manually tracking ICMP-only devices and their network position outside of OneUptime, since they don't appear in Topology at all currently.

Additional context This is related to two other filed requests: "Network Topology should include manually-added Ping-monitored devices, linked via labels" and the incorrect-link bug reported separately for SNMP-discovered devices ("Unmanaged neighbor" links). Together, these would let Topology represent the full network — SNMP-discovered, ICMP-discovered, and manually-added devices — with correct parent-child structure even where automatic discovery can't determine it.