Add proxy provider implementations

[ProphetLamb]

Proxies are not always usable, and sometimes your target blocks the proxy we're using.
This PR abstracts the IProxyProvider interface behind a validation layer.

1. Each IProxyProposalProvider produces a list of potential proxy server: API request here.
2. Each IProxyProposalValidator validates the proxy server and returns: Good, Bad, or Idk.
3. The ProxyProposalValidatorService BackgroundService periodically executes the validation of all sources. And always provides the latest list of validated proxies.

• For each proposed WebProxy:
  • if no validation returns Bad
  • add to the list of validated proxies
  • otherwise; log and skip

5. The ValidatedProxyProvider IProxyProvider integrates the system into the existing infrastructure. It simply returns the current list of the ProxyProposalValidatorService.

The PR adds dependencies to Microsoft.Extension.Hosting for the BackgroundService and Microsoft.Extensions.Configuration.Abstraction for the IOption<T> interface

ToDo

• Add integration into the Service fluent builder.
• Add ASP.NET integration
• Add option to periodically restart puppeteer with the next proxy configuration.