Add warning when peer_id is not available when building topology (#2140)
... see https://github.com/paritytech/polkadot-sdk/issues/2138 for why is not good, until we fix it let's add a warning to understand if this is happening in the wild. --------- Signed-off-by: Alexandru Gheorghe <[email protected]> Co-authored-by: Bastian Köcher <[email protected]>