java: Create issues for creating mentor notes for Java side exercises

I have gone through all of the core exercises and made sure that we either
(1) already have mentor notes or
(2) have an issue to create them

It would be best if we had a bug for all of them, but the manual work makes me want to take a breather and get back to it once we finish getting mentor notes for all of the core exercises (since that takes priority).

After we have finished up creating mentor notes for the core exercises, we should move onto the side exercises and this issue should stand as a reminder of that intention until someone (possibly a later version of myself) has time to add issues for the rest of them.