Rename deletions_object_storage.md to 202012_deletions_object_storage.md

Author: kakkoyun

docs/proposals/deletions_object_storage.md renamed to docs/proposals/202012_deletions_object_storage.md

@@ -105,4 +105,4 @@ Reasons for not choosing 4 i.e., **Custom format global - appendable file**:
 *   Have a max waiting duration feature for performing deletions where a default value is considered if explicitly not specified by the user. (only after this time passes the deletions are performed by the compactor in the next compaction cycle)
 *   Have the undoing deletions feature and there are two proposed ways
     *   API to undelete a time series - maybe delete the whole tombstones file?
-    *   “Imaginary” deletion that can delete other tombstones
+    *   “Imaginary” deletion that can delete other tombstones