chore: env management overhaul

[AdityaHegde]

We have multiple places where we read .env and assign variables for secrets. This leads to fragmented code especially with the new ducklake form changes.

Adding a service to manage env variables.

1. EnvStore manages the full list of variables. Has hooks for getter and setter so that in future we can separate the file write and admin API calls.
2. EnvEditSession manages the variables in flight during an edit. Managed which variables are assigned so that new env vars that come during the add data process is not overwritten.
3. This also allows for yaml construction and env assignment to happen in a single method, compileConnectorYAML. This makes things like ducklake utils to not worry about env, just focus on attach.

Checklist:

• Covered by tests
• Ran it and it works as intended
• Reviewed the diff before requesting a review
• Checked for unhandled edge cases
• Linked the issues it closes
• Checked if the docs need to be updated. If so, create a separate Linear DOCS issue
• Intend to cherry-pick into the release branch
• I'm proud of this work!