fix: treat unset PASSBOLT_PLUGINS_JWT_AUTHENTICATION_ENABLED as true

[0nelight]

What this PR does

Ensures the default value of PASSBOLT_PLUGINS_JWT_AUTHENTICATION_ENABLED (True) is set so that the JWT key pair is generated at container initialization. This ensures the Docker setup mirrors the default JWT authentication setup behavior found in bare-metal installations. fixes #243

Before
Keys were only generated if the env var was explicitly set to "true".

After

• Unset → treated as true (keys generated if missing)
• Explicit "true" → same as before
• "false" / empty / other → no generation

Why needed
The default value true for JWT Authentication (set in defaults.php) does not apply to the bash entrypoint/healthcheck scripts in Docker images. We must explicitly mirror this default in the bash logic to match bare-metal behavior in containerized deployments.

Changes

• Added unset check (-z "${VAR+xxx}") to the condition
• Added proper quoting for all variables (safer against special chars)
• No change when the var is explicitly set

[CLAassistant]

All committers have signed the CLA.

[LouisVallat]

Hey 👋,
Thank you for the PR and the good description,
Although it was a correct suggestion, we wanted to refactor a bit of the surrounding code 🖖

Thank you again,
Louis