Make a way to integrate `mail` app with `integration_openproject`

Is your feature request related to a problem? Please describe.

We have a nextcloud app integration_openproject through which we can create workpackages (basically a ticket) from nextcloud it self. As of now we can create the workpackage by filling a form through integration_openproject itself. But we want to integrate integration_openproject with the mail app so that we can create a workpackage from the all the content of a email in the mail app when our app is enabled.

Describe the solution you'd like

I am not sure of having a proper solution but one thing that could be done is that the mail app could have some hooks through which from the integration_openproject application we can inject some code so that the mail app can have an action to create a workpackage from mail app whenever intgeration_openproject is enabled.

Describe alternatives you've considered

or if there is other solution that can be considered would be really appreciated for it to make the things work.

The issue names no files, tests, or entry points. Start by reviewing how integration_openproject currently creates workpackages and how the mail app exposes message actions, then agree on an extension point; done means the mail app can offer creation from an email when the integration is enabled.