Add environment to chainlet DeploymentContext

[spal1]

Needed to revert my previous changes because they were not compatible with older context builder versions #1213

🚀 What

Adds an environment parameter to the chainlet DeploymentContext which can be accessed in a chainlet's __init__.
The environment of a chainlet can now be accessed by doing the following:

def __init__(
    self,
    # Adding the `context` argument, allows us to access the environment
    context: chains.DeploymentContext = chains.depends_context(),
) -> None:
    self._environment: Optional[definitions.Environment] = context.environment   

We need to add the environment field to DeploymentContext in a backwards-compatible manner, which is why it defaults to None in this PR. We can clean this up once dev, staging, and production are on a truss context builder version that includes these changes.

Backwards-compatibility test (using production's default context builder version)
Ran poetry run truss chains push truss-chains/truss_chains/example_chainlet.py

[linear]

BT-12428 Add `environment` to `chains.DeploymentContext`