feat: add support for secret environment files

[hbenali]

This commit introduces support for managing sensitive environment variables using secret files in the eXo Platform Docker image.

• Environment variables prefixed with EXO_SEC_ and suffixed with _FILE are read from the specified file paths.
• The file contents are exported as standard environment variables for use by the application.
• Enables secure handling of passwords, API keys, and private keys without hardcoding them in Docker commands or Compose files.

Example usage:

• EXO_SEC_DB_PASSWORD_FILE=/run/secrets/exo_db_password
• EXO_SEC_MAIL_SMTP_PASSWORD_FILE=/run/secrets/exo_mail_smtp_password

[bourasom]

LGTM

[bourasom]

if both envs (with SEC and without) are put, is there a priority? Shall We add test on that?

[houssemexo26]

if both envs (with SEC and without) are put, is there a priority? Shall We add test on that?

Yes, direct environment variables should take priority over file-based secrets. This is the standard pattern in containerized environments (Docker Compose, Kubernetes). Added tests to verify:

1. Direct variable > file secret when both exist

2. File loads only when the direct variable is absent

3. _FORCE flag allows override when needed

The priority logic prevents secrets from accidentally overriding explicit configuration and makes behavior predictable. Tests will catch regressions.