Clean up 'attachment service' names to storage controller (#7326)

The binary etc were renamed some time ago, but the path in the source
tree remained "attachment_service" to avoid disruption to ongoing PRs.
There aren't any big PRs out right now, so it's a good time to cut over.

- Rename `attachment_service` to `storage_controller`
- Move it to the top level for symmetry with `storage_broker` & to avoid
mixing the non-prod neon_local stuff (`control_plane/`) with the storage
controller which is a production component.

.dockerignore

@@ -22,6 +22,7 @@
 !s3_scrubber/
 !safekeeper/
 !storage_broker/
+!storage_controller/
 !trace/
 !vendor/postgres-*/
 !workspace_hack/