Improve ADF version references in main template (#351)

* Improve ADF version references in main template

**Why?**

For each new version of ADF, we need to update the version number in the
main template. However, as there are quite a few, it is likely to forget
one or search/replace another string that should not have matched.

**What?**

By adding the version number as a mapping, it can be updated quickly.
Reducing the number of times the version is repeated in the template to
two.

The first usage, in the Serverless Application Repository (SAR) metadata
is not able to use intrinsic CloudFormation functions unfortunately.
As described in the
[SAR Metadata property documentation](https://docs.aws.amazon.com/serverless-application-model/latest/developerguide/serverless-sam-template-publishing-applications-metadata-properties.html).

* Use version metadata on new Version parameter too

src/template.yml

@@ -16,6 +16,10 @@ Metadata:
     HomePageUrl: https://github.com/awslabs/aws-deployment-framework
     SemanticVersion: 3.1.2
     SourceCodeUrl: https://github.com/awslabs/aws-deployment-framework
+Mappings:
+  Metadata:
+    ADF:
+      Version: 3.1.2
 Parameters:
   CrossAccountAccessRoleName:
     Type: String
@@ -193,7 +197,7 @@ Resources:
           TERMINATION_PROTECTION: false
           MASTER_ACCOUNT_ID: !Ref AWS::AccountId
           ORGANIZATION_ID: !GetAtt Organization.OrganizationId
-          ADF_VERSION: 3.1.2
+          ADF_VERSION: !FindInMap ['Metadata', 'ADF', 'Version']
           ADF_LOG_LEVEL: INFO
       FunctionName: StackWaiter
       Role: !GetAtt LambdaRole.Arn
@@ -214,7 +218,7 @@ Resources:
           DEPLOYMENT_ACCOUNT_BUCKET: !GetAtt SharedModulesBucketName.Value
           MASTER_ACCOUNT_ID: !Ref AWS::AccountId
           ORGANIZATION_ID: !GetAtt Organization.OrganizationId
-          ADF_VERSION: 3.1.2
+          ADF_VERSION: !FindInMap ['Metadata', 'ADF', 'Version']
           ADF_LOG_LEVEL: INFO
       FunctionName: DetermineEventFunction
       Role: !GetAtt LambdaRole.Arn
@@ -235,7 +239,7 @@ Resources:
           DEPLOYMENT_ACCOUNT_BUCKET: !GetAtt SharedModulesBucketName.Value
           MASTER_ACCOUNT_ID: !Ref AWS::AccountId
           ORGANIZATION_ID: !GetAtt Organization.OrganizationId
-          ADF_VERSION: 3.1.2
+          ADF_VERSION: !FindInMap ['Metadata', 'ADF', 'Version']
           ADF_LOG_LEVEL: INFO
       FunctionName: CrossAccountExecuteFunction
       Role: !GetAtt LambdaRole.Arn
@@ -254,7 +258,7 @@ Resources:
           S3_BUCKET_NAME: !Ref BootstrapTemplatesBucket
           TERMINATION_PROTECTION: false
           MASTER_ACCOUNT_ID: !Ref AWS::AccountId
-          ADF_VERSION: 3.1.2
+          ADF_VERSION: !FindInMap ['Metadata', 'ADF', 'Version']
           ADF_LOG_LEVEL: INFO
       FunctionName: RoleStackDeploymentFunction
       Role: !GetAtt LambdaRole.Arn
@@ -273,7 +277,7 @@ Resources:
           S3_BUCKET_NAME: !Ref BootstrapTemplatesBucket
           TERMINATION_PROTECTION: false
           MASTER_ACCOUNT_ID: !Ref AWS::AccountId
-          ADF_VERSION: 3.1.2
+          ADF_VERSION: !FindInMap ['Metadata', 'ADF', 'Version']
           ADF_LOG_LEVEL: INFO
       FunctionName: MovedToRootActionFunction
       Role: !GetAtt LambdaRole.Arn
@@ -292,7 +296,7 @@ Resources:
           S3_BUCKET_NAME: !Ref BootstrapTemplatesBucket
           TERMINATION_PROTECTION: false
           MASTER_ACCOUNT_ID: !Ref AWS::AccountId
-          ADF_VERSION: 3.1.2
+          ADF_VERSION: !FindInMap ['Metadata', 'ADF', 'Version']
           ADF_LOG_LEVEL: INFO
       FunctionName: UpdateResourcePoliciesFunction
       Role: !GetAtt LambdaRole.Arn
@@ -472,7 +476,7 @@ Resources:
         Image: "aws/codebuild/standard:5.0"
         EnvironmentVariables:
           - Name: ADF_VERSION
-            Value: 3.1.2
+            Value: !FindInMap ['Metadata', 'ADF', 'Version']
           - Name: TERMINATION_PROTECTION
             Value: false
           - Name: PYTHONPATH
@@ -736,7 +740,7 @@ Resources:
     Type: Custom::InitialCommit
     Properties:
       ServiceToken: !GetAtt InitialCommitHandler.Arn
-      Version: 3.1.2
+      Version: !FindInMap ['Metadata', 'ADF', 'Version']
       RepositoryArn: !GetAtt CodeCommitRepository.Arn
       DirectoryName: bootstrap_repository
       ExistingAccountId: !Ref DeploymentAccountId
@@ -775,7 +779,7 @@ Resources:
       ServiceToken: !GetAtt CrossRegionBucketHandler.Arn
       Region: !Ref DeploymentAccountMainRegion
       BucketNamePrefix: !Sub "adf-shared-modules-${DeploymentAccountMainRegion}"
-      Version: 3.1.2
+      Version: !FindInMap ['Metadata', 'ADF', 'Version']
       PolicyDocument:
         Statement:
           - Action:
@@ -959,7 +963,7 @@ Resources:
           Id: adf-codepipeline-trigger-bootstrap
 Outputs:
   ADFVersionNumber:
-    Value: 3.1.2
+    Value: !FindInMap ['Metadata', 'ADF', 'Version']
     Export:
       Name: "ADFVersionNumber"
   LayerArn: