Add Modbus cover (#33642)

* Add Modbus cover

* Fix improper commands written for Modbus cover via coil

* Make changes per review comments

* Fix default hub not defined

Since support for multiple hubs was added, the default hub option
was not implemented correctly. Now I added necessary logic to make
it work. First hub in a list will be used as a default hub.

* Move Cover config under Modbus section

* Revert setting up a default hub alias

* Make hub mandatory for Cover

* Add default scan interval

* Read scan_interval from discovery info

* Fix linter error

* Use default scan interval from Cover platform

* Handle polling for Modbus cover directly inside entity

* Move covers under hub config

* Fix for review comment

* Call update() from Cover actuator methods

* Fix time validation