<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:

def list_capability_definitions(service_instance=None):
    '''
    Returns a list of the metadata of all capabilities in the vCenter.

    service_instance
        Service instance (vim.ServiceInstance) of the vCenter.
        Default is None.

    .. code-block:: bash

        salt '*' vsphere.list_capabilities
    '''
    profile_manager = salt.utils.pbm.get_profile_manager(service_instance)
    ret_list = [_get_capability_definition_dict(c) for c in
                salt.utils.pbm.get_capability_definitions(profile_manager)]
    return ret_list