## Proposed Changes
In this change I've added a new beacon_node cli flag `--execution-jwt-secret-key` for passing the JWT secret directly as string.
Without this flag, it was non-trivial to pass a secrets file containing a JWT secret key without compromising its contents into some management repo or fiddling around with manual file mounts for cloud-based deployments.
When used in combination with environment variables, the secret can be injected into container-based systems like docker & friends quite easily.
It's both possible to either specify the file_path to the JWT secret or pass the JWT secret directly.
I've modified the docs and attached a test as well.
## Additional Info
The logic has been adapted a bit so that either one of `--execution-jwt` or `--execution-jwt-secret-key` must be set when specifying `--execution-endpoint` so that it's still compatible with the semantics before this change and there's at least one secret provided.
242ae21e5d