Bump govuk_content_models to 24.2.0

This adds support for the 'latest_change_note' and 'public_timestamp'
fields to the Artefact model.

A dependency change in 24.1.0 requires at least version 10.0.0 or above
of gds-sso, so the gem has been updated here too.
Include change information when indexing artefacts

This changes the RummageableArtefact model to include the 
'public_timestamp' and 'latest_change_note' fields when rendering an
artefact to be sent to Rummager.
Merge pull request #234 from alphagov/send-public-timestamp-and-change-note-to-rummager

Send public timestamp and change note to rummager
Make specialist_sector_cleanup non-interactive

So that we can run the task easily using Fabric, we need to remove the
interactivity from the `specialist_sector_cleanup` Rake task.

The task performs only one operation, so the removal of interactivity is 
not a significant functionality regression.

I've also added some additional output in cases where the sector slug is
not provided.
Merge pull request #235 from alphagov/de-interactivize-sector-cleanup-task

Make specialist_sector_cleanup non-interactive
Bump govuk_content_models to v25.0.0

This is to stop us saving `Edition` objects with the
`alternative_title` field present.
Merge pull request #236 from alphagov/bump-content-models-to-v25

Bump govuk_content_models to v25.0.0