Improve MIME Type Handling for Content-Disposition Header

[marevol]

In this update, we're introducing a configuration to Fess that allows setting the Content-Disposition header to 'inline' based on MIME types. The main changes include:

• Adding the capability to configure inline display for specific MIME types (application/pdf, text/plain).
• Refactoring the code to retrieve the charset and inline MIME types more efficiently.

These changes aim to provide more flexibility and control over how content is displayed based on its MIME type.