Add accelerate as extra for transformers library

[EthanBunce]

Describe your changes

Added accelerate as extra for transformers in finetune llm template

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• I updated CHANGELOG.MD with a description of my changes
• If the change was to a module, I ran the code validation script (scripts/validate.sh)
• If the change was to a module, I have added thorough tests
• If the change was to a module, I have added/updated the module's README.md
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By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[malachi-constant]

AWS CodeBuild CI Report

• CodeBuild project: AIOpsModuleTestsInfrastruct-doMLXEYsnmxr
• Commit ID: d96f5f3
• Result: SUCCEEDED
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[clokep]

To cross-link, I removed this in #206 as I was mistaken that it was unused. From conversations with @EthanBunce we realized that transformers uses it automatically if is installed. Adding it back as an extra will hopefully make it clear that we don't use it directly, but still want it installed.