This pull request introduces a new feature to the application: the ability to convert Outlook .msg files into markdown format by extracting email metadata and content. The implementation adds a new class, OutlookMsgConverter, which extends the DocumentConverter base class.

Key Features
Email Metadata Extraction:
Extracts and includes key headers like From, To, Subject in the markdown output.

Email Body Conversion:
Reads the email body content and formats it into markdown.

Robust Encoding Support:
Attempts to decode content in UTF-16 first, falling back to UTF-8 and handling edge cases to ensure accurate conversion.

Implementation Details
File Validation:
Checks the file extension (.msg) before proceeding with the conversion.

Stream Parsing:
Uses olefile to parse the .msg file structure, extracting streams for headers and body content.

Error Handling:
Includes comprehensive exception handling to manage invalid files or unexpected errors during the conversion process.

Please review the implementation and provide feedback or suggestions for improvement.