chore: Rename references to Storage Manager in docs to File Uploader

[jordanvn]

Description of changes

• Updates docs pages to reference File Uploader instead of Storage Manager
• Changes page path to /fileuploader
• Adds deprecation warning for Storage Manager
• Updates message in GH templates

To Do:

• Update use of StorageManager to FileUploader (relies on changes in https://github.com/aws-amplify/amplify-ui/pull/5696)

Note: theming, and

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Checklist

• [x] Have read the Pull Request Guidelines
• [x] PR description included
• [x] yarn test passes and tests are updated/added
• [x] PR title and commit messages follow conventional commit syntax
• [ ] If this change should result in a version bump, changeset added (This can be done after creating the PR.) This does not apply to changes made to docs, e2e, examples, or other private packages.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.