This PR supports enables ManagerBasedRLEnv to properly support
gymnaisum's composite observation gym.spaces.Dict at term-level with
proper min, max specification. The benefit is that this will give
rl-library a clearer signs how to pre-process the obseravtion data.

Before:
All terms are assigned with `gym.Spaces.Box(min=-np.inf, max=np.inf)`,
one problem with this is that from rl-library side, is that some
rl-libraries network construction depends heavily on observations space
details. RL-library (e.g. sb3) looks at `gym.Spaces.Box.min` and
`gym.Spaces.Box.max` to determine if they need to normalize it at
library side.

After:
this PR utilizes on obs_terms's clip to determine if gym.Spaces.Box
should be stricter. For example, environment obs_term returning
gym.Spaces.Box(min=0, max=255) will be automatically detected by sb3,
and a proper scalling be applied automatically. whereas
gym.Spaces.Box(min=-inf, max=inf) will fail.

while no special case is treated for gym.Spaces.Box(min=-1, max=1), but
this will makes the rl-library easy to figure out that this term is
already clipped, not more transformation needed.

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Signed-off-by: Kelly Guo <kellyg@nvidia.com>
Co-authored-by: Kelly Guo <kellyg@nvidia.com>