[configuration] Add diagnosis trajectory help text

[CamilleBeau]

Brief summary of changes

This PR adds that "diagnosis evolution trajectory" can be edited in the configuration help text, and also adds a help text file for the diagnosis evolution config settings page.

Testing instructions (if applicable)

1. Go to the configuration module
2. Click the question mark icon at the top right to see the help text
3. Make sure that the help text includes that you can edit diagnosis evolution trajectory
4. Go to edit diagnosis evolution trajectory
5. Click on the question mark icon at the top right to see the help text
6. Check that the help text properly gives information on the diagnosis evolution trajectory page

Link(s) to related issue(s)

• Resolves [configuration] Add "Diagnosis Trajectory" to help text #10642