When features are not useful, or even documented, it's a good idea to remove them and keep the code simpler.

Steps:

• Let's remove completely the feature provided by this INI setting:

; this action name is used when the URL ends with a slash /
; it is useful to have an actual string to write in the UI
action_default_name = index

• When removing this, the code introduced here: https://github.com/matomo-org/matomo/pull/12669/files#diff-25480e51390b4cbc5cf99a0721101188 can also be removed.

• Because the value was set to index by default, all archived data will include records with /index as the page URL. So after removing this feature, there will be two entries, one for /index and one for /. Maybe we could somehow merge/group the two rows together, and keep the data correct, this would be ideal to prevent confusion of having 2 rows for the same page.

Following up: #12669