Add local provider for the testing

[supercaracal]

I have a plan to implement benchmarking code for the performance tuning. But it seems that there is no easy way to do testing the server on local host. So I added a provider which serves local image files. We can access them via browser or so such that:

$ make run
$ curl -I 'http://localhost:3000/Lenna.jpg'
HTTP/1.1 200 OK
Server-Timing: f_load;dur=2.341667,f_decode;dur=65.713575,f_encode;dur=7.579446
Date: Fri, 24 Jan 2025 03:04:37 GMT
Content-Type: image/jpeg

It looks to me that the local_image_path setting is no longer used by any internal implementation.