Feat: Jumanji register manager

[WiemKhlifi]

What?

Implement a registry manager class for Jumanji environments. In this case, we check the existence of the given scenario and create the corresponding attributes to initialise the environment class.

Why?

This manager class and the accompanied functions help avoid creating numerous configuration files for each scenario (e.g. for RWARE and LBF).

How?

For the selected environment-scenario pair:

• we first check the existence of the JSON file jumanji_scenarios.json and then the existence of env_name with the scenario name.
• Create a limited number of scenarios and store them if env_name doesn't exist in the file keys. Otherwise, check if the scenario is valid and extract its attributes if it's already created or create them and add them to the JSON file.
• This JSON file will be automatically initialised for the given environment, making it easier to extract attribute names and values to create the env object.

Extra

Teaser: This also helps merge the gym and Jumanji configs for the two common environments used (this will be the focus of a separate PR).

Close #975.

[WiemKhlifi]

The problem is that for each Jumanji environment we add, we'll have to add a specific function to extract its attributes, which will increase the number of functions added. So we've decided to close this PR for now and use YAML configurations and treat this as an environment specification that hopefully can be handled in Jumanji itself in the future.

Changes will remain on the feat/jumanji_env_register branch for a while 🤞