chore: improve performance store attestation

[migmartri]

There were a couple of issues with storing attestations

• The go-routine was leaving some open connections, this was a regression introduced a couple of days ago.
• But these open connections were happening because of the referrer storage logic that was runnign a very long transaction. This code removes the transaction and simplifies the code.

before we were getting this

SELECT count(*) as total, usename AS username, state, query FROM pg_stat_activity where state = 'idle in transaction' group by (username, state, query);
 total | username  |        state        | query
-------+-----------+---------------------+-------
    50 | chainloop | idle in transaction | begin

refs #1533

[jiparis]

Is this an accidental change?

[migmartri]

not really, I uncommented it so we can reproduce locally the issues, and in the end I left it like this. Do you think we should remove it?