Add secret manager support

[moebiusband73]

Currently per default a .env file is loaded to initialize environment variables for secrets.
While this is fine for development it is potentially dangerous in production.

Solution:
Add a new package with a interface to initialize the environment.
Suggested initial implementations:

• none: if environment is set from outside, eg in a docker container
• env: Read a .env file
• infisical: Read environment from Open Source Infisical secret manager

Support for other secret managers can be added in the future.