frame pointer: use blob API commitment instead of block height and tx index

[tuxcanfly]

Currently the tx index is hardcoded to 0, as the submit_pfb endpoint does not return an index for the data we just submitted.

We should use a commitment to the data we just posted, either a coordinate in the EDS or a transaction hash so that the query is actually unique.

[tuxcanfly]

See: https://node-rpc-docs.celestia.org/#blob

[tuxcanfly]

Closing as fixed in v0.2.0-OP_v1.2.0-CN_v0.12.0