start value of Discrete spaces

[JoshuaBluem]

Description

This fixes the missing applying of start value of Discrete Space

The start value of "spaces.Discrete(3, start=-1)" has no effect and does not shift the space to given start value, even tough there are examples in the Discrete class like: observation_space = Discrete(3, start=-1, seed=42) # {-1, 0, 1}
All Discrete Spaces start currently at zero.

Motivation and Context

This is a bug-fix relating to #2052, #913, #1295, #1378

• I have raised an issue to propose this change (required for new features and bug fixes)

Types of changes

The start value of spaces.Discrete is added to the actions to properly shift space
Reason for this position is, its the same position, the final scaling of spaces.Box happen. spaces.Discrete was never handled

• Bug fix (non-breaking change which fixes an issue)
• [No] New feature (non-breaking change which adds functionality)
• [No] Breaking change (fix or feature that would cause existing functionality to change)
• [No] Documentation (update in the documentation)

Checklist

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• I have updated the changelog accordingly (required).
• [No] My change requires a change to the documentation.
• I have updated the tests accordingly (required for a bug fix or a new feature).
• [No] I have updated the documentation accordingly.
• [No] I have opened an associated PR on the SB3-Contrib repository (if necessary)
• [No] I have opened an associated PR on the RL-Zoo3 repository (if necessary)
• I have reformatted the code using make format (required)
• I have checked the codestyle using make check-codestyle and make lint (required)
• I have ensured make pytest and make type both pass. (required)
• I have checked that the documentation builds using make doc (required)

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