Update toml config in Synapse Handlers

[SanojPunchihewa]

Description:
The toml config given in the doc[1] is incorrect. It should be as follows,

[[synapse_handlers]]
name = "<handlerName>"
class = "<packageName>.<handlerName>"

[1] - https://mi.docs.wso2.com/en/latest/develop/customizations/creating-synapse-handlers/

[DinithiDiaz]

Closing as completed.