Handle blockchain oplog

Some data will go to onchain oplog instead of indexer oplog (see https://forum.duniter.org/t/oplog-onchain-vs-offchain/12328):

• transaction comments
• network-related data (endpoints...)
• spam-proof profile creation

Duniter-squid will index the onchain data if it is in clear, but only cids if it is on ipfs.

Datapods can retreive this ipfs data and index content. This could be used for example for a full-text search in offchain transaction comments.