feat: add database manager with per plugin config

This commit introduces:
- a new backwards compatible database manager which allows the end-user
  to set global and per plugin database configuration.
- an early iteration of a database connector interface.
- provides helper functions for each of the database connectors to
  meet the new interface.

Signed-off-by: Minn Soe <contributions@minn.io>

packages/backend/src/index.ts

@@ -29,7 +29,7 @@ import {
   getRootLogger,
   loadBackendConfig,
   notFoundHandler,
-  SingleConnectionDatabaseManager,
+  PluginConnectionDatabaseManager,
   SingleHostDiscovery,
   UrlReaders,
   useHotMemoize,
@@ -59,7 +59,7 @@ function makeCreateEnv(config: Config) {
 
   root.info(`Created UrlReader ${reader}`);
 
-  const databaseManager = SingleConnectionDatabaseManager.fromConfig(config);
+  const databaseManager = PluginConnectionDatabaseManager.fromConfig(config);
   const cacheManager = CacheManager.fromConfig(config);
 
   return (plugin: string): PluginEnvironment => {