pipeline: run method takes store object not dir

Instead of passing the store directory to Pipeline.run, pass an
already initialized ObjectStore object. This binds the lifetime
of the store and its (temporary) objects to the run of osbuild
not the run of the pipeline.
This prepares re-using the stores with multiple (non-nested)
pipelines.

osbuild/main_cli.py

@@ -14,6 +14,7 @@ import sys
 import osbuild
 import osbuild.meta
 import osbuild.monitor
+from osbuild.objectstore import ObjectStore
 from osbuild.formats import v1 as fmt
 
 
@@ -114,12 +115,13 @@ def osbuild_cli():
     monitor = osbuild.monitor.make(monitor_name, sys.stdout.fileno())
 
     try:
-        r = manifest.build(
-            args.store,
-            monitor,
-            args.libdir,
-            output_directory=args.output_directory
-        )
+        with ObjectStore(args.store) as object_store:
+            r = manifest.build(
+                object_store,
+                monitor,
+                args.libdir,
+                output_directory=args.output_directory
+            )
     except KeyboardInterrupt:
         print()
         print(f"{RESET}{BOLD}{RED}Aborted{RESET}")