Add POST/DELETE methods for certain CMAPI REST endpoints

CMAPI claims REST compliance (official documentation: "...CMAPI ... is a REST API that can be used to manage a multi-node Enterprise ColumnStore cluster"), but some of the documented calls deviate from the REST specification:

• The call to add a new cluster member is defined as PUT to /.../cluster/add-node - this call should use POST method as it creates a new resource.

• The call to remove a cluster member is defined as PUT to /.../cluster/remove-node - this call should use DELETE method with path like /.../cluster/remove-node/NODE_ID as it removes an existing resource.