Use environment variable for `from` about website-stalker

[EdJoPaTo]

This actually worked in the past but was removed in 4d5e390.

Seeing the value of from as a secret is an interesting point. Not sure how to improve the situation in a good way.
In my mind I am thinking about integrations for notifications (Slack, Telegram, Mail, …) which would also be configured in some way. These are also secrets and need to be configured.

I am not sure how to handle them in a good way while maintaining simplicity and easy to understand GitHub Actions.
With multiple notification targets this can easily end up in a bunch of secrets.

I will test around what a simple but good solution for this might be. Thanks for bringing this up!

[EdJoPaTo]

I added this back in 94e4bd4 which will be part of v0.16.0.

This can be used to override a config value:

export WEBSITE_STALKER_FROM=my-email-address