Improve max event limit count to be passed to frontend

What is the issue

• The max limit for Cycle Analytics events is a hardcoded value in the backend and frontend

Solution

• Pass the MAX_EVENTS to the frontend to be used in the limit_warning_component.js

Reasons

• Improve the testability of limit warning component
• Reduce the chance these values get out of sync

Related MRs

Add limit to the number of events showed in cycle analytics | gitlab-ce!7743
Resolve "Add event limit warning to all Cycle Analytics tabs" | gitlab-ce!10179

/cc @filipa @grzesiek