feat: return Content-Type header with the mimeType of the file

[pentreathm]

Description

Please include a summary of the change and which issue is fixed/closed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Closes # (issue)

Changes

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i.e.

• Removed method X from class Y
• Return 400 instead of 500 in Z case
• Refactored class X into a new module

Types of changes

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• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change). If there's an API change, link the pull request in the API spec repository and the accepted DAO governance poll
• I have read the CONTRIBUTING document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.