Add GroupAndRoleSeparationEnabled config to docs

[npamudika]

Description:
Due to the newly added role group seperation feature [1] which is in IS, starting from 5.11.0 version, we need to disable the GroupAndRoleSeparationEnabled config as below in the IS_HOME/repository/conf/deployment.toml file as below when configuring IS as KM following [2].

[authorization_manager.properties]
GroupAndRoleSeparationEnabled = false

At APIM we have handled this internally, but at IS side, we have added it explicitly. When migrating from an older version we are handling this in the migration process as well [3].

[1] wso2/product-is#8123
[2] https://apim.docs.wso2.com/en/4.1.0/install-and-setup/setup/distributed-deployment/configuring-wso2-identity-server-as-a-key-manager/
[3] https://github.com/wso2-enterprise/migration-docs/blob/main/api-manager/migration-docs/is-as-a-km/is-5.11.0/Upgrade%20IS%20as%20Key%20Manager%205.9.0%20to%20IS%205.11.0%20for%20APIM%203.0.0%20to%204.1.0.md

Affected Product Version:
APIM 4.1.0 and above