Clarify when memory stores are being used
Clarify when memory stores are being used

This adds logging for the cases where memory only stores are being used. It also
reorganises the sync store path to match the crypto store.

Part of https://github.com/vector-im/riot-web/issues/9309

matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk,matrix-org/matrix-react-sdk