ENH Add a warning if allowed hosts is not set.

[GuySartorelli]

Also adds ability to "wildcard" allow all hosts, which disables the logging, and some much needed test coverage.

Issue

• Warn developers if SS_ALLOWED_HOSTS has not been set #11610

[GuySartorelli]

I chose to do this as a protected method because the fact that bootConfigs() is called from BaseKernel is an implementation detail of that kernel - other kernels could be implemented to intentionally avoid calling that method, so this allows them a way to still perform this validation.

This also provides a clear place for this sort of validation to be done for other config in the future, if we find a need to do so.

[emteknetnz]

Works well

[emteknetnz]

Actually noticed that the non-env method of setting this doesn't appear to work correctly - with the following config I get warnings logged and I'm able to access my site which doesn't have an example.com style domain

I've copied the config from the docs for the logging, and from the docs PR for the allowed hosts

SilverStripe\Core\Injector\Injector:
  Psr\Log\LoggerInterface:
    calls:
      LogFileHandler: [ pushHandler, [ '%$LogFileHandler' ] ]
  LogFileHandler:
    class: Monolog\Handler\StreamHandler
    constructor:
      - "/var/www/silverstripe.log"
      - "info"
  SilverStripe\Control\Middleware\AllowedHostsMiddleware:
    properties:
      AllowedHosts:
        - 'example.com'
        - 'www.example.com'
        - 'subdomain.example.com'

[GuySartorelli]

Looks like you're missing the after directive

---
after: requestprocessors
---
SilverStripe\Core\Injector\Injector:
  SilverStripe\Control\Middleware\AllowedHostsMiddleware:
    properties:
      AllowedHosts:
        - 'example.com'
        - 'www.example.com'
        - 'subdomain.example.com'

[emteknetnz]

Yup that fixed it