fix: send bytes instead of bytes of string

[saihaj]

while debugging issue on some other subgraph found that we were storing the base64 that was because it was converting String -> bytes but we want to store the bytes directly so we can use the Bytes type in subgraphs to show the Hex value nicely

context: https://guild-oss.slack.com/archives/C03B2US85J4/p1688395836580659?thread_ts=1688359311.715519&cid=C03B2US85J4

[maoueh]

Let's not change the proto definition, there is just too much chance of uncovered breaking change.

Let's just fix the graph_out to emit the right thing.