docs: add samples for soft delete (objects)

[JesseLovelace]

Samples for working with soft deleted objects, intended for https://cloud.google.com/storage/docs/use-soft-delete and https://cloud.google.com/storage/docs/use-soft-deleted-objects

[snippet-bot]

Here is the summary of changes.

You are about to add 6 region tags.

• samples/snippets/src/main/java/com/example/storage/bucket/DisableSoftDelete.java:19, tag storage_disable_soft_delete
• samples/snippets/src/main/java/com/example/storage/bucket/GetSoftDeletePolicy.java:19, tag storage_get_soft_delete_policy
• samples/snippets/src/main/java/com/example/storage/bucket/SetSoftDeletePolicy.java:19, tag storage_set_soft_delete_policy
• samples/snippets/src/main/java/com/example/storage/object/ListSoftDeletedObjects.java:19, tag storage_list_soft_deleted_objects
• samples/snippets/src/main/java/com/example/storage/object/ListSoftDeletedVersionsOfObject.java:19, tag storage_list_soft_deleted_object_versions
• samples/snippets/src/main/java/com/example/storage/object/RestoreSoftDeletedObject.java:19, tag storage_restore_object

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[sydney-munro]

approved with 2 small comments.

[sydney-munro]

approved with 2 small comments.

LGTM