ENG-484 Add export formats to `secrets env` command

Should be an option.

Feature Summary: Export Option for secrets env

This feature introduces an --env-export flag to the secrets env command, allowing it to handle environment variables in a way that ensures compatibility with child processes across multiple platforms.

Key Functionalities

1. Unix Format

Previous Behavior:

Environment variables were output as:

ENV_VAR="value"

This format sets variables but does not export them, meaning they are not available to child processes unless explicitly exported.

New Behavior with --env-export:

export ENV_VAR="value"

Adding the export prefix ensures that the variables are propagated to child processes. This is essential for scripts requiring child processes to inherit these variables.

2. Windows PowerShell

With --env-export:

Variables are set as global or session-specific based on context:

$env:ENV_VAR = 'value'

Without --env-export:

Variables are scoped only to the current PowerShell session:

$ENV_VAR = 'value'

Dynamic Updates:

The variables are immediately updated in the current session and optionally persist globally based on the flag.

3. Windows CMD

Default Behavior:

Variables are set using set commands, which inherently propagate to child processes:

set ENV_VAR=value

New Behavior:

No additional export mechanism is needed since CMD already ensures propagation of variables to child processes.