mgr/dashboard: fix image size in nvmeof namespace create/update api

mgr/dashboard: fix image size in nvmeof namespace create/update api

- Different name is used in POST and PATCH for `rbd_image_size`
- Using same name in both requests
- fixing typing issues in frontend

Fixes https://tracker.ceph.com/issues/69864

Signed-off-by: Afreen Misbah <afreen@ibm.com>
(cherry picked from commit 7fa78e62a456bd706dafd6fd30568dfd88acf3b4)

 Conflicts:
	src/pybind/mgr/dashboard/frontend/src/app/ceph/block/nvmeof-namespaces-form/nvmeof-namespaces-form.component.ts
	src/pybind/mgr/dashboard/frontend/src/app/shared/api/nvmeof.service.spec.ts
	src/pybind/mgr/dashboard/frontend/src/app/shared/api/nvmeof.service.ts
        - restore it to the request type where groups is not present