[AWS::EC2::AccountSetting] - [Coverage] - Missing CloudFormation support

### Name of the resource

Other

### Resource name

AWS::EC2::AccountSetting

### Description

There are various APIs which can modify EC2 Account settings:

- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_ModifyDefaultCreditSpecification.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_EnableImageBlockPublicAccess.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DisableImageBlockPublicAccess.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_GetImageBlockPublicAccessState.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_EnableSnapshotBlockPublicAccess.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DisableSnapshotBlockPublicAccess.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_GetSnapshotBlockPublicAccessState.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_ModifyInstanceMetadataDefaults.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_GetInstanceMetadataDefaults.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_EnableAllowedImagesSettings.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DisableAllowedImagesSettings.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_GetAllowedImagesSettings.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_EnableSerialConsoleAccess.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_GetSerialConsoleAccessStatus.html
- https://docs.aws.amazon.com/AWSEC2/latest/APIReference/API_DisableSerialConsoleAccess.html

and probably more, but nothing like `AWS::EC2::AccountSetting` exists in CloudFormation.

### Other Details

See `AWS::SSM::ServiceSetting`, it is already possible for another AWS Service to configure Account configurations through CloudFormation, so this should be considered tech debt of AWS since it is missing for `AWS::EC2::AccountSetting`.

Start by comparing the existing AWS::SSM::ServiceSetting resource with the listed EC2 account-setting APIs and their AWS documentation. Done means defining and implementing CloudFormation support for the relevant AWS::EC2::AccountSetting configuration, with coverage for the required account-setting operations.

Written by the indexing model from the issue text.