Thanks for reaching here! Indexers operate at the container level so there's not a way to define an indexer to loop through all blob containers. Generally, you can create an indexer per storage container. Depending on how many containers you have, this can become difficult though (services have limits to the number of indexers you can have).
Assuming you have a manageable number of containers, its recommended you create your first indexer in the portal and then use a tool like postman or our vs code extension to quickly create the additional data sources and indexers required. You can have multiple indexers all point to the same index.
Let us know if further query.