Raise awareness of version upgrade strategies

[sbrannen]

After we release a new version of JUnit 5, there are always users who encounter issues while upgrading the JUnit versions used in the projects.

As @scordio pointed out in #3933 (comment), we should raise awareness of the available version upgrade strategies.

Places we could that:

• Release Notes
• project README page
• new issue overview page
• new issue templates
• pinning a related issue with an obvious issue title

[mpkorstanje]

It might be worth while to have the JUnit Platform check at startup if all its dependencies are at the right version. And if not, log a warning that directs people to the documentation.

People typically don't read documentation up front, but they do read error messages.