add FileTypeDetector

[febner]

No description provided.

[jarnaiz]

Hello Franz!

First of all, thanks for your time doing this pr.

I dont understand the final purpose of this change... I think is a good point to use the ServiceLoader to load the Tika module, but if we dont use the class com.upplication.s3fs.util.FileTypeDetector in the library itself, why implement it?
Im working in a branch with your code trying to use the class but I dont want to open the InputStream twice in the method sync.
Look at:

S3FileChannel#sync()
S3SeekableByteChannel#sync()

I like the idea to use the method Files.probeContentType() in the sync method and add the option to override the implementation with another class. Like #41 suggested.

But Im not sure how to do it exactly..