Fix JWT secret file handling in Nethermind entrypoint

[DeVikingMark]

• Add missing directory creation for JWT secret file
• Use consistent JWT_SECRET_FILE variable instead of undefined OP_NODE_L2_ENGINE_AUTH

[cb-heimdall]

🟡 Heimdall Review Status

Requirement	Status	More Info
Reviews	🟡 0/1	Denominator calculation Show calculation 1 if user is bot 0 1 if user is external 0 From .codeflow.yml 1 Additional review requirements Show calculation Max 0 0 From CODEOWNERS 0 Global minimum 0 Max 1 1 1 if commit is unverified 0 Sum 1

[kaspro183]

“This was just a test PR, nothing malicious intended

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.