Support GitHub Environment Secrets for Easier Secret Management

Currently, this action requires all secrets to be placed in a single `.env` file, which is then copied into a single GitHub Secret. This approach presents several challenges:

- Updating a single secret requires overwriting all secrets, meaning all secrets must be maintained locally or recreated from scratch.
- Teams must keep a copy of the `.env` file outside of GitHub, which is difficult to manage and synchronize across different team members.
- This is because modifying secrets in a granular way via the GitHub UI is not possible, you may only overwrite them.

## Proposed Solution

It would be beneficial if this action could support GitHub **Environment Secrets** as an alternative method for secret management. This would allow developers to specify the name of the environment from which secrets and variables should be read.

## Benefits
- **Granular Secret Management** – Secrets can be updated individually without affecting others.
- **Improved Security** – Avoids the need to store `.env` files locally.
- **Better Team Collaboration** – No need to sync `.env` files manually.
- **Leverages Native GitHub Features** – Aligns with best practices for GitHub Actions.