Directory Listing: Add UTF-8 Charset to the response Content type

[alexkutsan]

Within the directory listing handler, the absence of an explicit charset in the content type has led to issues, particularly with directories containing non-ASCII symbols, resulting in broken displays.

Adding charset charset=UTF-8 to the Content-type header fixes this issue.

Alternate Designs

• Add <meta charset="UTF-8"> to https://github.com/crystal-lang/crystal/blob/master/src/http/server/handlers/static_file_handler.html
• Add charset as an optional parameter to serve_static config

Benefits

it works

Possible Drawbacks

Not flexible for non UTF-8 cases.

[alexkutsan]

Seams like this part of code is a monkey patched crystal std lib. Added similar PR to original crystal code https://github.com/crystal-lang/crystal/pull/14546