Add our new open source plugins as submodules

[tsteur]

We recently launched OAuth2 and MCP Server as free open source plugins.
Just like the other plugins, can we add those as submodules please?
I believe this may also help with documentation so that we generated documentation for those if they expose APIs on developer.matomo.org. For example, we will likely soon expose some events for other plugins to hook into.
Not sure if there have been other new open source plugins recently.

Problem: Both plugins require PHP 8.1 so that might not work. Possible we need to do this with Matomo 6

[sgiehl]

Actually with Matomo 6 I would more likely try to get rid of all plugin submodules that are not directly bundled with core.
We should look into a solution to automatically run tests for all our plugins with each core PR or similar.
But having the submodules actually causes more friction and pain, than it has any benefits (apart from running the tests)

[tsteur]

We could alternatively review whether to ship all open-source plugins with core. Originally, they weren't in core because storage was limited etc. Nowadays, there is probably not too many good reasons not to ship it with core. We could make the features more discoverable in Matomo.

• This way all tests at least for these features would run directly and less internet be needed to activate the plugin.
• It would be also a slightly more similar experience on Cloud and On-Premise (eg simplifying docs).
• Some plugins like OAuth, MCP, Custom Alerts, MS Teams, Slack could be activated by default and improve experience and consistency with Cloud. Such features wouldn't clutter the UI if activated by default.
• Plugins team could still maintain them and merge them
• From a development point certain refactorings/changes be easier

New plugins that we release more often could start on Marketplace and be incorporated into core after few months.
Tests may run a bit longer but that could be okay given the better user experience and noticing issues sooner (saving time in return).
I'll add this for discussion to next TAC