feat: New Command Simplify to Modify Templates to Use Fn::ForEach

[elishacatherasoo]

Description of changes:
This new command can modify templates to use the new Fn::ForEach function. Right now it can modify basic templates with only one property that is different in Resources/Outputs/Conditions.

How to use: rain simplify --foreach ../path/to/template.yaml

An example of a template that can be modified is shown below.

Unprocessed template:

AWSTemplateFormatVersion: 2010-09-09
Transform: 'AWS::LanguageExtensions'
Resources:
  DynamoDBTable1:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table1
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable2:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table2
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable3:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table3
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable4:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table4
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable5:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table5
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable6:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table6
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable7:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table7
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable8:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table8
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable9:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table9
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'
  DynamoDBTable10:
    Type: 'AWS::DynamoDB::Table'
    Properties:
      TableName: Table10
      AttributeDefinitions:
        - AttributeName: id
          AttributeType: S
      KeySchema:
        - AttributeName: id
          KeyType: HASH
      ProvisionedThroughput:
        ReadCapacityUnits: '5'
        WriteCapacityUnits: '5'

Processed template:

AWSTemplateFormatVersion: "2010-09-09"

Transform: AWS::LanguageExtensions

Resources:
  Fn::ForEach::Loop0:
    - Variable0
    - - Table1
      - Table10
      - Table2
      - Table3
      - Table4
      - Table5
      - Table6
      - Table7
      - Table8
      - Table9
    - Resource${Variable0}:
        Properties:
          AttributeDefinitions:
            - AttributeName: id
              AttributeType: S
          KeySchema:
            - AttributeName: id
              KeyType: HASH
          ProvisionedThroughput:
            ReadCapacityUnits: "5"
            WriteCapacityUnits: "5"
          TableName: !Ref Variable0
        Type: AWS::DynamoDB::Table

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[ericzbeard]

I wonder if this would be better as an addition to the fmt command, instead of adding a new top level command. rain fmt --foreach is more specific than rain simplify. Unless we had some more ideas for ways that we could simplify templates (fmt already converts intrinsics to short form, which is a minor simplification).

Can you point me to the code that figures out what resources have been duplicated? I was finding it a little hard to follow the flow of the code from the top down, maybe you could add a comment section somewhere that describes the overall design of the feature.

I noticed a few code blocks that look like they were copied from other areas in the project, it would be good if we could refactor/reuse rather than copy, for example simplify.String.