DEV: Improve phpBB3 import script (#15956)

* Optional import of custom user fields from phpBB 3.1+
* Optional import of likes from phpBB3
  Requires the phpBB "Thanks for posts" extension
* Fix import of bookmarks from phpBB3
* Update `created_at` of existing user
* Support mapping of phpBB forums to existing Discourse categories
  This is in addition to the ability of merging phpBB forums and importing into newly created Discourse categories.

script/import_scripts/phpbb3/settings.yml

@@ -36,20 +36,25 @@ import:
 
   # Category mappings
   #
-  # For example, topics from phpBB category 1 and 2 will be imported
-  # in the new "Foo Category" category, topics from phpBB category 3
-  # will be imported in subcategory "Bar category", topics from phpBB
-  # category 4 will be merged into category 5 and category 6 will be
-  # skipped.
+  # * "source_category_id" is the forum ID in phpBB3
+  # * "target_category_id" is either a forum ID from phpBB3 or a "forum_id"
+  #   from the "new_categories" setting (see above)
+  # * "discourse_category_id" is a category ID from Discourse
+  # * "skip" allows you to ignore a category during import
   #
-  # category_mappings:
-  #   1: foo
-  #   2: foo
-  #   3: bar
-  #   4: 5
-  #   6: SKIP
+  # Use "target_category_id" if you want to merge categories and use
+  # "discourse_category_id" if you want to import a forum into an existing
+  # category in Discourse.
   #
-  category_mappings: {}
+  #  category_mappings:
+  #    - source_category_id: 1
+  #      target_category_id: foo
+  #    - source_category_id: 2
+  #      discourse_category_id: 42
+  #    - source_category_id: 6
+  #      skip: true
+  #
+  category_mappings: []
 
   # Tag mappings
   #
@@ -122,6 +127,9 @@ import:
   private_messages: true
   polls: true
 
+  # Import likes from the phpBB's "Thanks for posts" extension
+  likes: false
+
   # When true: each imported user will have the original username from phpBB as its name
   # When false: the name of each imported user will be blank unless the username was changed during import
   username_as_name: false
@@ -134,3 +142,12 @@ import:
     # here are two example mappings...
     smiley: [':D', ':-D', ':grin:']
     heart: ':love:'
+
+  # Map custom profile fields from phpBB to custom user fields in Discourse (works for phpBB 3.1+)
+  #
+  #  custom_fields:
+  #    - phpbb_field_name: "company_name"
+  #      discourse_field_name: "Company"
+  #    - phpbb_field_name: "facebook"
+  #      discourse_field_name: "Facebook"
+  custom_fields: []