Port RabbitMQ URL placeholder description and custom builders/formatters doc updates

[SanojPunchihewa]

Description

We need to port RabbitMQ URL placeholder description and custom builders/formatters doc update [1] to the following versions.

https://apim.docs.wso2.com/en/4.2.0/install-and-setup/setup/mi-setup/message_builders_formatters/message-builders-and-formatters/

https://mi.docs.wso2.com/en/4.2.0/install-and-setup/setup/message-builders-formatters/message-builders-and-formatters/

https://mi.docs.wso2.com/en/4.3.0/install-and-setup/setup/message-builders-formatters/message-builders-and-formatters/

https://mi.docs.wso2.com/en/4.4.0/install-and-setup/setup/message-builders-formatters/message-builders-and-formatters/

[1] - #1870

Version

No response