Restructure project layout and add ECR repository CloudFormation template

- Move application entrypoint to cmd/lambda/
- Move Dockerfile to docker/ for clearer build context separation
- Promote go.mod/go.sum to project root
- Move CloudFormation templates under infra/cfn/ for consistent infra layout
- Add new template-container-repository.yaml defining ECR repository (blog-deployment)
- Move Lambda test files to test/ directory

template-secret-key.yaml

@@ -1,26 +0,0 @@
-AWSTemplateFormatVersion: '2010-09-09'
-Transform: AWS::Serverless-2016-10-31
-Parameters:
-  WebhookSecret:
-    Type: String
-    Description: The number as a secret key of a webhook
-
-Resources:
-
-  SecretForWebhook:
-    Type: AWS::SecretsManager::Secret
-    Properties:
-      Description: The number as a secret key of a webhook
-      SecretString: !Sub 
-        - '{"secretNumber": "${WebhookSecret}"}'
-        - WebhookSecret: !Ref WebhookSecret
-      Tags: 
-        - Key: Project
-          Value: Git-server
-
-Outputs:
-  ArnSecretForWebhook:
-    Description: ARN of secret key of a webhook
-    Value: !Ref SecretForWebhook
-    Export:
-      Name: SecretForWebhook-ARN