Support config file

[eenagy]

Problem:

Lighthouse lacks support for a dedicated config file, unlike other Ethereum clients. Currently, configurations must be passed through command line flags or wrapper scripts.

Proposal:

Add support for a config file (e.g., lighthouse.conf/yaml) for both CL and validator clients.

Benefits:

Cleaner systemd service files
Easier configuration management
Consistent with other client implementations
Easy to share config files
Also easier to start each client (validator/cl)

[dapplion]

Supporting a config file is on the roadmap! We need to migrate to clap derive first. This effort is tracked here

• Implement Clap derive #5900

Then we can easily support a config file

[chong-he]

Seems to be related to the issue:
#4734
#2748