Notify updates to unapproved extensions

Overview

I've noticed that updates aren't flagged for some CiviCRM extensions. In this particular case we weren't being shown updates for the Transactional Emails Extension. I'm guessing that this is because this particular extension isn't approved for automated distribution.

I think it makes sense that some extensions aren't shown in the UI for installation, but if they have been installed and they are listed on civicrm.org I think the UI should flag when there is an update. I had presumed that the updates would show up so was surprised that they hadn't.

Current behaviour

System Status only shows available updates for extensions that are approved for automated distribution.

Updates for other extensions aren't shown so the user may assume that the extension is up to date.

Proposed behaviour

System Status shows available updates for all extensions that are listed on civicrm.org.

Comments

Potentially this could be extended to also show updates for extensions that aren't listed on civicrm.org but are publicly available on GitLab or GitHub.

Related issue #2548 (closed)

Workarounds

For those that can't wait for this to be implemented in core, there is an extension that provides this functionality here: https://lab.civicrm.org/extensions/allavailableupgrades

See also this post on StackExchange about a settings change that will show all available upgrades.