feat: add option to block custom components

[jordanrfrazier]

Adds a configurable flag to block custom component creation/execution and editing of components.

With LANGFLOW_ALLOW_CUSTOM_COMPONENTS=true, we keep the existing behavior. With false, we will

1. Block creation and execution of custom components - checked using the pre-built component index
2. UI changes to block Custom Component Creation
3. UI changes to block edits on Core Components

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✨ Finishing touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
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• Commit unit tests in branch add-option-to-block-custom-code

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[jordanrfrazier]

This needs more thought - the component index is static. At the least we'll need to build a historical hash index for backwards and forwards-compatibility.

More thought required to ensure no breaking changes.