[POC] Decouple Task enums from task classes

[matteobettini]

Here is the concept.

Tasks are enum like before, but now they are decoupled from their class.

This is similar to the way that ModelConfig-> Model works (one class for config and one class for component)
(same for algos)

Now this is the case also for tasks: you have an enum that holds the config and you can call get_task() to lock the config into a task class.

task1 = VmasTask.BALANCE.get_from_yaml() # Get from yaml automatically converts to TaskClass
task2 = VmasTask.BALANCE.get_from_yaml() # Get from yaml automatically converts to TaskClass
task1.config.update({"a": 1})
task2.config.update({"a": 2})
assert task1.config["a"] == 1
assert task2.config["a"] == 2

[itwasabhi]

Should these two functions be here? wouldnt it be possible for the config of a task to modify whether or not it supports a discrete action?

[itwasabhi]

Could add doc along the lines of:

Represents a specific environment that is to be constructed. 

The environment is fully defined by its constructor (TaskClass.get_env_fun) and its parameterization (TaskClass.config). 

Note that there could be a many-to-one mapping between TaskClasses and environments. For example: 
- A single TaskClass may allow construction of all environments of `PettingZoo`
- A single TaskClass may allow construction of environments of `PettingZoo` that only have discrete actions
- A single TaskClass may allow construction of just a specific `PettingZoo` environment.