feat(api-service): add endpoint to update api key with provided value

[4rthem]

What changed? Why was the change needed?

Add API endpoind to update API key of an environment.
Need to update the API key from the NOVU_SECRET_KEY env var.

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[scopsy]

@4rthem could you please share a little bit on your usecase for this? API Keys could not be updated, as they are auto generated by the system. (Could be regenerated tho)

[4rthem]

@scopsy We have a Docker Compose stack, and we need every service to be able to connect to each other (including Novu) as soon as they start. The issue with generated API keys is that we have to update the environment variables after the Novu environment is created. Instead, we need a predictable secret so that services can connect on the first run.

Ideally, Novu would honor a NOVU_SECRET_KEY or DEFAULT_NOVU_SECRET_KEY, similar to how other tools handle predefined secrets, for example:

• PostgreSQL with POSTGRES_PASSWORD
• Keycloak with KC_BOOTSTRAP_ADMIN_PASSWORD