fix: respect pre-set BASE_NODE_P2P_ADVERTISE_IP in consensus-entrypoint

[haileymarshall]

Fixes #1107

What changed?

consensus-entrypoint now only runs public IP discovery when BASE_NODE_P2P_ADVERTISE_IP is not already set. If the operator provided a value, the script logs it and uses it as-is. Behavior when the variable is unset is unchanged: discovery runs against the same four providers and a total failure still exits with code 8.

Why?

As reported in #1107, the script unconditionally called get_public_ip and then export BASE_NODE_P2P_ADVERTISE_IP=$PUBLIC_IP, which

1. silently overwrote any advertise IP the operator configured (NAT/proxy setups where the routable IP differs from the egress IP), and
2. made startup hard-fail with exit 8 on hosts with restricted egress to the four IP-echo services, even when the operator had already supplied the value discovery was meant to provide.

How has it been tested?

• bash -n syntax check.
• Exercised the guard with a stubbed curl in all three scenarios:
  • variable pre-set + discovery unreachable → keeps the operator value and continues (previously exit 8),
  • variable unset + discovery reachable → fetches and exports the discovered IP as before,
  • variable unset + discovery unreachable → still exits 8, unchanged.

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 2 if repo is sensitive 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1