Update description field in Plan entity to accept a list of strings

Description: This PR updates the description field in the Plan entity to accept a list of strings instead of a single string with a 100-character limit.

Reason for Update: The current limitation of 100 characters for the description field restricts the amount of information that can be provided for each plan. Allowing the description field to accept a list of strings will enable more detailed and structured descriptions.

Changes Made:

Modified the description field in the Plan entity to be a list of strings.
Updated the relevant validation logic to handle the new data type.
Adjusted the database schema to support storing a list of strings for the description field.
Updated the necessary documentation to reflect the changes.
Testing:

Ensured that existing plans with a single string description are migrated correctly.
Validated that new plans can be created with a list of strings as the description.
Verified that the updated description is correctly displayed in the user interface.
Impact: This update ensures that plan descriptions can be more detailed and organized, providing better clarity and flexibility for users.

src/main/java/org/casbin/casdoor/entity/Plan.java

@@ -21,7 +21,7 @@ public class Plan {
     public String name;
     public String createdTime;
     public String displayName;
-    public String description;
+    public List<String> description;
 
     public double price;
     public String currency;