r/api_management: support for sign_in, sign_up and policy blocks

[tombuildsstuff]

This PR adds support for the sign_in and sign_up settings blocks - and also adds support for the policy block, which was previously added as a separate resource by @JunyiYi in #3145 (I've rolled this up into this PR since it's only possible to have one per API, thus it makes more sense within this resource).

This is the last PR from our list covered in #1177 - as such this fixed #1177

[mbfrahry]

LGTM with a minor comment

[tombuildsstuff]

Tests pass:

[ghost]

This has been released in version 1.24.0 of the provider. Please see the Terraform documentation on provider versioning or reach out if you need any assistance upgrading. As an example:

provider "azurerm" {
	version = "~> 1.24.0"
}
# ... other configuration ...

[cpdohert]

Forgive me if I'm not understanding something about API management policies here, but there are four different scopes for APIM policies: global, product, API and API operation. We make heavy use of product-scoped policies and I was hoping to make use of terraform for this now that the api_management resource has been merged - but it doesn't seem like there's any way to do that with the policy block as implemented. Also, if it's true that there can only be one policy per API, doesn't it make more sense for the policy {} block to be implemented in api_management_api than api_management? Implementing it in api_management would imply global policy scope.

[tombuildsstuff]

@cpdohert this PR added support for Global Policies - we can look to add support for the other APIM policy resources but there’s no issue/feature request tracking them at the moment as far as I recall - would you mind opening a new issue for that?

[ghost]

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