`FileTypeRouter` should get mime type from `ByteStream` mime type attribute instead of `meta

[wochinge]

Describe the bug Looking at this code here:

The ByteStream class has an attribute mime_type. We should rather using this than using the metadata for this.

Error message None

Expected behavior Use mime_type field instead of meta (or make this configurable)

Additional context Add any other context about the problem here, like document types / preprocessing steps / settings of reader etc.

To Reproduce Steps to reproduce the behavior

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System:

• OS:
• GPU/CPU:
• Haystack version (commit or version number): 2
• DocumentStore:
• Reader:
• Retriever: