Addition of new graphs

[Vireth4114]

Checklist before requesting a review

• [x] I have performed a self-review of my code.
• [x] This change requires a documentation update.

Description

I have added two new graphs to the mreporting plugin:

• The first one, in Helpdesk, is a graph showing the evolution of ticket over a period with each year on top of each other
• The second one, in Helpdesk Plus, is a vertical stackbar showing for each employee, the time they took on ticket tasks each month

Screenshots: