* Non-repudiation: add persistent, SQL-backed signed commands repo Closes https://github.com/digital-asset/daml/issues/8634 Contributes to https://github.com/digital-asset/daml/issues/8658 changelog_begin changelog_end * Address https://github.com/digital-asset/daml/pull/8723#discussion_r569228934 * Fix issues after rebase, address https://github.com/digital-asset/daml/pull/8723#discussion_r569227969 * Fix certificate table and column names, add timestamp to persistent store, address https://github.com/digital-asset/daml/pull/8723#discussion_r569223780 * Fix outstanding compilation errors * Fix tests after rebase * Address comments from https://github.com/digital-asset/daml/pull/8723#pullrequestreview-582106893 - Address https://github.com/digital-asset/daml/pull/8723#discussion_r569216711 - Address https://github.com/digital-asset/daml/pull/8723#discussion_r569217401 * Address https://github.com/digital-asset/daml/pull/8723#discussion_r569215383
