How to pass args to initdb?

[Edit: My apologies, I realize now this belongs on the main postgres-operator issues board and have posted it there instead]

Hello, I need a database with initdb args --lc-collate=C and --lc-ctype=C for Matrix Synapse, and it's not entirely clear how to do so from the docs. Nothing I see in the CRD reference looks right -- PostgresCluster.spec.patroni only appears to cover dynamic config -- and I searched many forum & issue posts. Is there a way to get these arguments to initdb with a v5 PostgresCluster?