Add the possibility to modify the injection with the "properties" in the actions

[BDonnot]

Is your feature request related to a problem? Please describe.

To update the injection, you need to do:

act = env.action_space({"injection": {"load_p": 1.3 * self._init_load_p, "prod_p": 1.3 * gen_p}})
...

Describe the solution you'd like

I would like to be able to do it using the "properties", as for the others

act = env.action_space()
act.gen_p = ....
act.load_p = ....

Describe alternatives you've considered

Only the "old" syntax is supported, which is not very clear, nor convenient.

[BDonnot]

Will be integrated to next major release (2.0 most likely)