Azure App Configuration / Feature Flags

[Ryan-Palmer]

This PR closes #387

The changes in this PR are as follows:

• Azure App Config builder
• Feature Flag builder

I have read the contributing guidelines and have completed the following:

• Tested my code end-to-end against a live Azure subscription.
• Updated the documentation in the docs folder for the affected changes.
• Written unit tests against the modified code that I have made.
• Updated the release notes with a new entry for this PR.
• Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

I'll update docs and tests once the general implementation has been given the thumbs up.

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

open Farmer
open Farmer.Builders
open Farmer.Arm

let configStore =
    configurationStore {
        name "azConfigFarmerTest"
        sku ConfigSku.Developer
        feature_flags [
            {
                Name = "TestFlag"
                Description = "A test feature flag"
                Label = "Flag label"
                State = true
            }
            {
                Name = "TestFlag2"
                Description = "Another test feature flag"
                Label = ""
                State = false
            }
        ]
    }

let deployment = arm {
    location Location.NorthEurope
    add_resource configStore
}

deployment
|> Deploy.execute "test-farmer-config" Deploy.NoParameters
|> printfn "%A"