Added ability to use DockerBuildArgs in Amazon.Lambda.Tools serverless template.

Issue #, if available: #201

Description of changes: Added ability to use DockerBuildArgs in Amazon.Lambda.Tools serverless template. This change required implementation for both JSON and YAML template parsers.

Testing: Tested (in debug mode) using the following templates for sample https://github.com/aws/aws-extensions-for-dotnet-cli/tree/master/testapps/ImageBasedProjects/ServerlessTemplateExamples: JSON template:

{
  "AWSTemplateFormatVersion": "2010-09-09",
  "Transform": "AWS::Serverless-2016-10-31",
  "Description": "An AWS Serverless Application.",
  "Resources": {

    "UseDockerMetadataFunction": {
      "Type": "AWS::Serverless::Function",
      "Properties": {
        "MemorySize": 256,
        "Timeout": 30,
        "Policies": [
          "AWSLambdaBasicExecutionRole"
        ],
        "PackageType" : "Image",
        "ImageConfig" : {
            "Command" : "UseDockerMetadata::UseDockerMetadata.Function::FunctionHandler"
        }
      },
      "Metadata": {
        "Dockerfile": "Dockerfile.custom",
        "DockerContext": "./UseDockerMetadata",
        "DockerTag": "aws-extensions-tests:usedockermetadata",
        "DockerBuildArgs": {
          "PROJECT_PATH": "/src/path-to/project",
          "PROJECT_FILE": "project.csproj"
        }
      }
    }
  },

  "Outputs": {
  }
}

YAML template:

AWSTemplateFormatVersion: 2010-09-09
Transform: 'AWS::Serverless-2016-10-31'
Description: An AWS Serverless Application.
Resources:
  UseDockerMetadataFunction:
    Type: 'AWS::Serverless::Function'
    Properties:
      MemorySize: 256
      Timeout: 30
      Policies:
        - AWSLambdaBasicExecutionRole
      PackageType: Image
      ImageConfig:
        Command: 'UseDockerMetadata::UseDockerMetadata.Function::FunctionHandler'
    Metadata:
      Dockerfile: Dockerfile.custom
      DockerContext: ./UseDockerMetadata
      DockerTag: 'aws-extensions-tests:usedockermetadata'
      DockerBuildArgs:
        PROJECT_PATH: /src/path-to/project
        PROJECT_FILE: project.csproj
Outputs: {}

Output:

Amazon Lambda Tools for .NET Core applications (5.4.1)
Project Home: https://github.com/aws/aws-extensions-for-dotnet-cli, https://github.com/aws/aws-lambda-dotnet

Enter CloudFormation Stack Name: (CloudFormation stack name for an AWS Serverless application)
teststack
Enter S3 Bucket: (S3 bucket to upload the build output)
mappingNode.Children
Warning: Unable to determine region for bucket mappingNode.Children, assuming bucket is in correct region: The specified bucket does not exist
Processing CloudFormation resource UseDockerMetadataFunction
Initiate packaging of ./UseDockerMetadata for resource UseDockerMetadataFunction
Building Docker image for D:\source\repros\ServerlessTemplateExamples\./UseDockerMetadata
Inspecting Dockerfile to figure how to build project and docker image
Executing docker build
... invoking 'docker build', working folder 'D:\source\repros\ServerlessTemplateExamples\./UseDockerMetadata, docker file D:\source\repros\ServerlessTemplateExamples\./UseDockerMetadata\Dockerfile.custom, image name aws-extensions-tests:usedockermetadata'
... docker build  -f "D:\source\repros\ServerlessTemplateExamples\./UseDockerMetadata\Dockerfile.custom" -t aws-extensions-tests:usedockermetadata --build-arg PROJECT_PATH=/src/path-to/project --build-arg PROJECT_FILE=project.csproj .
... docker build: Sending build context to Docker daemon  228.9kB
... docker build: Step 1/3 : FROM public.ecr.aws/lambda/dotnet:5.0
... docker build: 5.0: Pulling from lambda/dotnet
... docker build: image operating system "linux" cannot be used on this platform
Error executing "docker build"

NOTE: The deployment fails due to incompatibility of Linux image while testing on Windows based environment, which is fine. The correct --build-arg(s) are passed to docker build call.

We need to add version bump commits in dev branch before actual release of queued changes.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

aws / aws-extensions-for-dotnet-cli

Added ability to use DockerBuildArgs in Amazon.Lambda.Tools serverless template. #219