chore: reduce log volume on server startup (#16608)

Addresses https://github.com/coder/coder/issues/16231.

This PR reduces the volume of logs we print after server startup in
order to surface the web UI URL better.

Here are the logs after the changes a couple of seconds after starting
the server:

<img width="868" alt="Screenshot 2025-02-18 at 16 31 32"
src="https://github.com/user-attachments/assets/786dc4b8-7383-48c8-a5c3-a997c01ca915"
/>

The warning is due to running a development site-less build. It wouldn't
show in a release build.

coderd/database/dbpurge/dbpurge.go

@@ -63,7 +63,7 @@ func New(ctx context.Context, logger slog.Logger, db database.Store, clk quartz.
 				return xerrors.Errorf("failed to delete old notification messages: %w", err)
 			}
 
-			logger.Info(ctx, "purged old database entries", slog.F("duration", clk.Since(start)))
+			logger.Debug(ctx, "purged old database entries", slog.F("duration", clk.Since(start)))
 
 			return nil
 		}, database.DefaultTXOptions().WithID("db_purge")); err != nil {