User Story:
As a Garden manager, I want the system to calculate the health index of a garden, so I can understand its health status and prioritize gardens for maintenance.

Acceptance Criteria:

• The garden's "Health Index" (CAMPX__Health_Index__c) field should be set based on this formula: ((Total Plant Count - Total Unhealthy Plant Count)/Total Plant Count) * 100
• The field must be recalculated and updated when there is a change in either the "Total Plant Count" or "Total Unhealthy Plant Count"
• The field should be 0 if the "Total Plant Count" is zero or blank
  
  

Example Scenario:

• In the garden, there are initially 50 total roses, 5 of which are unhealthy. After adding 5 new healthy roses, the "Health Index" is ((55 - 5) / 55) * 100 = 90.91.
• The Fern Garden has 40 total ferns, with 3 unhealthy. When another fern is marked unhealthy, the total unhealthy becomes 4. The "Health Index" is ((40 - 4) / 40) * 100 = 90.00.
• If all 10 plants in a Herb Garden are removed, the "Health Index" would be ((0 - 10) / 0) * 100 = 0.