Add track_blank_changes as default option

Time to start fixing some test failures instead of creating them. Add
track_blank_changes as a default option, defaulting to false.

  $ diff -u testresults/3-set-track_blank_changes.txt testresults/4-add-track_blank_changes-option.txt
  --- testresults/3-set-track_blank_changes.txt	2024-08-05 15:46:06.000000000 -0700
  +++ testresults/4-add-track_blank_changes-option.txt	2024-08-05 19:34:48.000000000 -0700
  @@ -504,7 +504,7 @@
  [...]
  -456 examples, 14 failures, 2 pending
  +456 examples, 8 failures, 2 pending
  [...]

The failures fixed are exactly the 6 introduced in commit 52cc180.

Author: BrianLMatthews

.rubocop_todo.yml

@@ -36,7 +36,7 @@ Metrics/BlockLength:
 # Offense count: 1
 # Configuration parameters: CountComments.
 Metrics/ClassLength:
-  Max: 120
+  Max: 121
 
 # Offense count: 6
 Metrics/CyclomaticComplexity:

lib/mongoid/history/options.rb

@@ -34,6 +34,7 @@ def default_options
           track_create: true,
           track_update: true,
           track_destroy: true,
+          track_blank_changes: false,
           format: nil }
       end