Validate configuration before execution

[TCFox]

Should be a valid connection string:

• AzureWebJobsStorage
• Azure:ServiceTokenProviderConnectionString

Should be LetsEncrypt, LetsEncrypt-Staging, or a valid URL for an ACME server:

• Acme:Server

Should be a valid and accessible Azure Subscription:

• Azure:Dns:SubscriptionId

Should be a valid and accessible Azure Resources:

• Azure:Dns:ResourceGroupName
• Azure:Dns:ZoneResourceName
• Azure:KeyVault:VaultName

Should be a valid email address:

• Acme:Account:EmailAddress

Should be a valid URL:

• Acme:Certificate:CommonName