[FEATURE REQUEST] batch and subset should be moved into the standard cmd methods

[whytewolf]

Is your feature request related to a problem? Please describe.
current batch and subset have their own api interfaces. cmd_batch and cmd_subset. these 2 functionalities lack a method for async calling them. which leads to issues if you want to use these features with salt-api or other python methods.

this means to use batch or subset we cannot follow the recommended best practice
https://docs.saltproject.io/en/latest/ref/netapi/all/salt.netapi.rest_cherrypy.html#best-practices

Describe the solution you'd like
move batch and subset into cmd, and cmd_*, and depreciate cmd_batch and cmd_subset

Describe alternatives you've considered
an alternative was to add async methods for both batch and subset, but his seems least viable.