When enabled, the CTFE IssuanceChainStorage feature attempts to INSERT a row into the IssuanceChain table for every single add-chain and add-pre-chain request. Often a duplicate key exception will be raised, in which case CTFE will ignore it; however, each time such an exception is raised on the database server, an error of the following form is added to the PostgreSQL log file:

2025-03-14 19:09:48.407 UTC [79887] ctlog@ctlog ERROR: duplicate key value violates unique constraint "issuancechain_pkey"
2025-03-14 19:09:48.407 UTC [79887] ctlog@ctlog DETAIL: Key (identityhash)=(\x75fd98459142f4ad8a38a620c728d994057d980ab64a44190badccd265dd4d4a) already exists.
2025-03-14 19:09:48.407 UTC [79887] ctlog@ctlog STATEMENT: INSERT INTO IssuanceChain(IdentityHash, ChainValue) VALUES ($1, $2)

Since these "errors" are expected to occur and do not represent an actual problem, it's not useful or desirable to log them.

This PR stops adds ON CONFLICT DO NOTHING to the INSERT statement, so that no exception is raised and these errors will not appear in the PostgreSQL log file.

Checklist

• I have updated the CHANGELOG.
  • Adjust the draft version number according to semantic versioning rules.
• I have updated documentation accordingly.