Move to tertiary navigation in Moodle 4

[t-schroeder]

Currently in Moodle 4 this plugin adds itself in the secondary navigation. So you end up with one entry for "Course completion" and one for "Course recompletion":

In the interest of keeping the secondary navigation short I'd suggest adding it instead to the tertiary navigation (i.e. the dropdown at the top) on the "Course completion" page:

[danmarsden]

I hear where you're going there but I'd worry about doing that on stable releases - but yes I do think it would probably make sense to move both the recompletion and modify course completion dates pages to the tertiary nav on the course completion page - but, moving links into tertiary navigation risks stuff like this:
https://moodle.org/mod/forum/discuss.php?d=451477

which could compound a lot more if we did it on the stable branches.... :-)

[danmarsden]

I wonder if we should add a new config setting that changes where it sits - by default it could drop it into the tertiary navigation and we could write an upgrade step that checks "does the site have any existing recompletions set" and if so, enable the setting to show it in the secondary nav so that existing sites won't find the link moving and getting lost?

would be great if someone wanted to fire through a PR to do this!