storage retain policy on sandbox vs branch

[ykethan]

Environment information

System:
  OS: macOS 14.7
  CPU: (8) arm64 Apple M1
  Memory: 195.31 MB / 16.00 GB
  Shell: /opt/homebrew/bin/fish
Binaries:
  Node: 20.11.1 - ~/.local/share/nvm/v20.11.1/bin/node
  Yarn: 1.22.21 - ~/.local/share/nvm/v20.11.1/bin/yarn
  npm: 10.8.2 - ~/.local/share/nvm/v20.11.1/bin/npm
  pnpm: 9.10.0 - ~/Library/pnpm/pnpm
NPM Packages:
  @aws-amplify/auth-construct: 1.3.1
  @aws-amplify/backend: 1.5.0
  @aws-amplify/backend-auth: 1.2.0
  @aws-amplify/backend-cli: 1.2.9
  @aws-amplify/backend-data: 1.1.4
  @aws-amplify/backend-deployer: 1.1.5
  @aws-amplify/backend-function: 1.7.0
  @aws-amplify/backend-output-schemas: 1.3.0
  @aws-amplify/backend-output-storage: 1.1.2
  @aws-amplify/backend-secret: 1.1.4
  @aws-amplify/backend-storage: 1.2.1
  @aws-amplify/cli-core: 1.1.3
  @aws-amplify/client-config: 1.4.0
  @aws-amplify/deployed-backend-client: 1.4.1
  @aws-amplify/form-generator: 1.0.3
  @aws-amplify/model-generator: 1.0.8
  @aws-amplify/platform-core: 1.1.0
  @aws-amplify/plugin-types: 1.3.0
  @aws-amplify/sandbox: 1.2.3
  @aws-amplify/schema-generator: 1.2.4
  aws-amplify: 6.6.5
  aws-cdk: 2.162.1
  aws-cdk-lib: 2.162.1
  typescript: 5.6.3
AWS environment variables:
  AWS_STS_REGIONAL_ENDPOINTS = regional
  AWS_NODEJS_CONNECTION_REUSE_ENABLED = 1
  AWS_SDK_LOAD_CONFIG = 1
No CDK environment variables

Describe the feature

the storage is currently set to destroy by default

amplify-backend/packages/backend-storage/src/construct.ts

Line 121 in 10ef35d

removalPolicy: RemovalPolicy.DESTROY,

in sandbox this makes sense as there may be lot of changes on the resource which can be destructive but on a branch deploy this should be set to retain

note:
you can override this on backend.ts

backend.storage.resources.bucket.applyRemovalPolicy(RemovalPolicy.RETAIN);

Use case

This would enable users to prevent loosing their data/bucket on a branch or production if there was a unexpected destructive action