use a single bucket rather than one per conversion

deploy/docker-compose.yml

@@ -23,6 +23,7 @@ services:
     environment:
       S3_ENDPOINT: ${S3_ENDPOINT:-seaweedfs:8333}
       S3_PUBLIC_ENDPOINT: ${S3_PUBLIC_ENDPOINT:-localhost:8333}
+      S3_BUCKET: ${S3_BUCKET:-officeconvert}
       S3_USE_SSL: ${S3_USE_SSL:-false}
       S3_ACCESS_KEY: ${S3_ACCESS_KEY:-minioadmin}
       S3_SECRET_KEY: ${S3_SECRET_KEY:-minioadmin}