Environment-Variable for self-hosted instances

[patschi]

I think it might be a good additional to implement a specific environment variable for self-hosted instances, to be able to do certain things differently. I think you, Plausible team, are using basically the same code 1:1 for your cloud instance and this could help for self-hosted instances.

To give an example:

1. Handling CRON_ENABLED (issue Q: cron for self-hosted instances? #400)
   

   analytics/config/config.exs

   Lines 102 to 109 in 039480a

   	cron_enabled = String.to_existing_atom(System.get_env("CRON_ENABLED", "false"))
   	base_cron = [
   	# Daily at midnight
   	{"0 0 * * *", Plausible.Workers.RotateSalts}
   	]
   	extra_cron = [

   
   In this case the CRON_ENABLED environment could be default to true for self-hosted scenarios.

2. Disable cronjob trial_notification_emails
   For example trial_notification_emails: As those emails are not really useful for self-hosted instances, this cronjob could be disabled when the self-hosted env variable is set.
   

   analytics/config/config.exs

   Line 131 in 039480a

   trial_notification_emails: 1,

3. Disable cronjob provision_ssl_certificates
   

   analytics/config/config.exs

   Line 127 in 039480a

   provision_ssl_certificates: 1,

4. Branding
   At certain places (emails, footer, etc) there's Plausible.io-related branding. While branding/credits are fine, those could be replaced to the admin's email address once self-hosted instance is in use.

[ukutaht]

@patschi Spot on, I've been thinking about doing something like this as well. I will probably add it for the next release