Add AWSSDK.Signin dependency to resolve AWS CLI v2 'aws login' credentials

The AWS SDK for .NET v4 resolves credentials from the AWS CLI v2 'aws login'
SSO flow via SigninServiceClientHelpers, which reflectively loads the
AWSSDK.Signin assembly at runtime. Without an explicit package reference the
assembly is absent from the tool output, causing credential resolution to fail
with "Assembly AWSSDK.Signin could not be found or loaded".

Fixes #1010

Author: dscpinheiro

.autover/changes/820ce536-653c-4f85-ba25-38489fd67ff2.json

@@ -0,0 +1,11 @@
+{
+  "Projects": [
+    {
+      "Name": "AWS.Deploy.CLI",
+      "Type": "Patch",
+      "ChangelogMessages": [
+        "Added AWSSDK.Signin dependency to resolve AWS credentials when authenticated using the AWS CLI v2 'aws login' SSO flow"
+      ]
+    }
+  ]
+}

src/AWS.Deploy.CLI/AWS.Deploy.CLI.csproj

@@ -29,6 +29,7 @@
     <PackageReference Include="AWSSDK.IdentityManagement" Version="4.0.9.10" />
     <PackageReference Include="AWSSDK.CloudFormation" Version="4.0.8.11" />
     <PackageReference Include="AWSSDK.SecurityToken" Version="4.0.5.12" />
+    <PackageReference Include="AWSSDK.Signin" Version="4.0.1.1" />
     <PackageReference Include="AWSSDK.SSO" Version="4.0.2.16" />
     <PackageReference Include="AWSSDK.SSOOIDC" Version="4.0.3.17" />
     <PackageReference Include="Swashbuckle.AspNetCore.Annotations" Version="6.5.0" />