Include Functionality for Hashicorp Vault

### Component

Securing Secrets and Keys

### Is your proposal related to a problem?

No

### Describe the solution you'd like

Looking for a mechanism to load secrets such as Hasura Admin keys, EE licenses and secrets from a file (secret mount) at runtime rather than injecting them as ENV Vars which is a security concern for sensitive information leakage.

Would be great to get a fromFile option supported which could be pointed to a secret mount or a location at runtime which ideally be integrated with AWS secrets manager or Hashicorp Vault or K8s secrets etc.

### Describe alternatives you've considered

N/A

No files, tests, or entry points are named. Start by locating the existing environment-variable handling for Hasura Admin keys, EE licenses, and secrets; done should include a defined fromFile mechanism that supports runtime secret mounts and the proposed AWS Secrets Manager, Hashicorp Vault, or Kubernetes secret sources.

Written by the indexing model from the issue text.