This issue depends on #793.

After Runtime Secrets Injection (Environment Variables) is implemented - we also should inject secrets as files.

Sub-issues:

• Implement secrets injection as files
• Implement unit-tests
• Extend API-level tests:
  • Make sure that GetManifest API returns secrets with file injection metadata.
• Implement agent-level tests:
  • Make sure that when agent initializes and retrieves Manifest with specified secrets - it creates/updates corresponding files accordingly.
• If possible implement e2e-tests. But it requires further research.
• Manually test secrets injection (as files)