AWS::ElasticBeanstalk::Environment - OptionSettings: Updates Can Remove Manually Added Environment Variables

## 1. Title

`AWS::ElasticBeanstalk::Environment-OptionSettings`: Updates Can Remove Environment Variables

## 2. Scope of request

AWS::ElasticBeanstalk::Environment-OptionSettings - aws:elasticbeanstalk:application:environment

## 3. Expected behavior

In Create or Update, a AWS::ElasticBeanstalk::Environment-OptionSettings - change should not

remove aws:elasticbeanstalk:application:environment environment variables added outside of CloudFormation (the present behavior) - the behavior when updating other resources (i.e. a S3 bucket) with property outside of CloudFormation is to leave these properties alone

but rather could:

- warn the user that environment variables (`aws:elasticbeanstalk:application:environment` values) will be removed
- allow the user to control the behavior using `reset` (where all `OptionSettings` are returned to values in CloudFormation stack), `updateoradd` (where all `OptionSettings` are updated or added and existing configuration is left untouched)
- have a documentation update here (https://docs.aws.amazon.com/AWSCloudFormation/latest/UserGuide/aws-properties-beanstalk-environment.html#cfn-beanstalk-environment-optionsettings) where `OptionSettings` documentation is updated to reflect manually created environment variables will be removed.
- do something else

Feel free to describe other desired and relevant implementation details.

## 4. Suggest specific test cases

To test this:

### create a CloudFormation stack using the template below

```
---

AWSTemplateFormatVersion: 2010-09-09

Description: AWS CloudFormation Stack for Running ElasticBeanstalk.

Parameters: {}

Mappings: {}

Resources:

VPC:
Type: AWS::EC2::VPC
Properties:
CidrBlock: 10.0.0.0/24

InternetGateway:
Type: AWS::EC2::InternetGateway

PublicInternetRoute:
Type: AWS::EC2::Route
Properties:
DestinationCidrBlock: 0.0.0.0/0
GatewayId: !Ref InternetGateway
RouteTableId: !Ref PublicInternetRouteTable

VPCGatewayAttachment:
Type: AWS::EC2::VPCGatewayAttachment
Properties:
InternetGatewayId: !Ref InternetGateway
VpcId: !Ref VPC

PublicInternetRouteTable:
Type: AWS::EC2::RouteTable
Properties:
VpcId: !Ref VPC

PublicSubnet01:
Type: AWS::EC2::Subnet
Properties:
AvailabilityZone: !Select [ 0, !GetAZs "" ]
CidrBlock: 10.0.0.0/25
VpcId: !Ref VPC

PublicSubnet02:
Type: AWS::EC2::Subnet
Properties:
AvailabilityZone: !Select [ 1, !GetAZs "" ]
CidrBlock: 10.0.0.128/25
VpcId: !Ref VPC

PublicSubnet01RouteTableAssociation:
Type: AWS::EC2::SubnetRouteTableAssociation
Properties:
RouteTableId: !Ref PublicInternetRouteTable
SubnetId: !Ref PublicSubnet01

PublicSubnet02RouteTableAssociation:
Type: AWS::EC2::SubnetRouteTableAssociation
Properties:
RouteTableId: !Ref PublicInternetRouteTable
SubnetId: !Ref PublicSubnet02

ElasticBeanstalkApplication:
Type: AWS::ElasticBeanstalk::Application
Properties:
# note that if ApplicationName is set and is not unique you
# will not able able to run a given stack multiple times
ApplicationName: !Ref AWS::StackName

ElasticBeanstalkIAMRole:
Type: AWS::IAM::Role
Properties:
AssumeRolePolicyDocument:
Version: 2012-10-17
Statement:
- Effect: Allow
Principal:
Service: ec2.amazonaws.com
Action: sts:AssumeRole
ManagedPolicyArns:
- arn:aws:iam::aws:policy/AWSElasticBeanstalkWebTier

ElasticBeanstalkInstanceProfile:
Type: AWS::IAM::InstanceProfile
Properties:
Roles:
- !Ref ElasticBeanstalkIAMRole

ElasticBeanstalkConfigurationTemplate:
Type: AWS::ElasticBeanstalk::ConfigurationTemplate
Properties:
ApplicationName: !Ref ElasticBeanstalkApplication
OptionSettings:
- Namespace: aws:autoscaling:asg
OptionName: MinSize
Value: 1
- Namespace: aws:autoscaling:asg
OptionName: MaxSize
Value: 1
- Namespace: aws:autoscaling:launchconfiguration
OptionName: IamInstanceProfile
Value: !Ref ElasticBeanstalkInstanceProfile
- Namespace: aws:autoscaling:launchconfiguration
OptionName: InstanceType
Value: t3.micro
- Namespace: aws:elasticbeanstalk:application:environment
OptionName: CITY
Value: SAN_FRANCISCO
- Namespace: aws:elasticbeanstalk:application:environment
OptionName: STATE
Value: CALIFORNIA
- Namespace: aws:elasticbeanstalk:environment
OptionName: EnvironmentType
Value: LoadBalanced
- Namespace: aws:elasticbeanstalk:environment
OptionName: LoadBalancerType
Value: application
- Namespace: aws:ec2:vpc
OptionName: VPCId
Value: !Ref VPC
- Namespace: aws:ec2:vpc
OptionName: Subnets
# Value: !Join turns the individual subnets into a string
Value: !Join [ ",", [ !Ref PublicSubnet01, !Ref PublicSubnet02 ] ]
- Namespace: aws:ec2:vpc
OptionName: AssociatePublicIpAddress
Value: true
SolutionStackName: 64bit Amazon Linux 2 v3.1.5 running PHP 7.4

ElasticBeanstalkEnvironment:
Type: AWS::ElasticBeanstalk::Environment
Properties:
ApplicationName: !Ref ElasticBeanstalkApplication
Description: AWS ElasticBeanstalk Environment
# EnvironmentName must be greater than or equal to 4 (you can't use "QA")
EnvironmentName: !Sub ${AWS::StackName}
# TemplateName: with environments where every element is exactly the same
# you may be able to use a single AWS::ElasticBeanstalk::ConfigurationTemplate
TemplateName: !Ref ElasticBeanstalkConfigurationTemplate
```

The create the stack using a command similar to the following: `aws cloudformation create-stack --stack-name EBwithEnvVars --capabilities CAPABILITY_IAM --template-body file://elasticbeanstalk_with_envvars.yaml`

### update an OptionSetting _outside_ of CloudFormation

Example: _outside_ of CloudFormation add an environment variable or c:
```
Namespace: aws:elasticbeanstalk:application:environment:
OptionName: COUNTRY
Value: UNITED_STATES
```

### modify an OptionSettings property and run an "Update Stack" using a command similar to the below:

Example: change the following:

```
Namespace: aws:autoscaling:launchconfiguration
OptionName: InstanceType
Value: t3.micro
```
then run the following:
`aws cloudformation update-stack --stack-name EBwithEnvVars --capabilities CAPABILITY_IAM --template-body file://elasticbeanstalk_with_envvars.yaml`

### confirm the _manually_ add Environment Variable has been removed

Configuration of environment variables outside of CloudFormation have been removed - in the case above this would have removed the environment variable `COUNTRY`.

## 5. Helpful Links to speed up research and evaluation

NA

## 6. Category

Use the categories as displayed in the AWS Management Console (simplified):

1. Compute

## 7. Any additional context

I'm not sure what the correct behavior should be... I know that existing changes made outside of CloudFormation _are not_ removed (i.e. a property on an S3 bucket) and I know that any change that results in configuration removal is surprising behavior.

Start by reproducing the behavior with the provided CloudFormation template, the aws cloudformation create-stack command, and the subsequent update-stack command for AWS::ElasticBeanstalk::Environment OptionSettings. Review the linked OptionSettings documentation and determine which handling of manually added environment variables is intended; done requires an agreed behavior and corresponding implementation or documentation change.

Written by the indexing model from the issue text.