Provide configurable Cache-Control header for static files

[jeevatkm]

Goal is achieve configurable Cache-Control header for static files.

• Default cache header
• Mime type wise Cache-Control configuration

[jeevatkm]

static file cache configuration in aah.conf:

cache {
  static {
    # Default `Cache-Control` for all static files,
    # if specific mime type is not defined.
    default_cache_control = "public, max-age=31536000"

    # (Optional) Define by mime types, if mime is not present then default is applied.
    # Config is very flexible to define by mime type.
    #
    # Create a unique name and provide `mime` with comma separated value
    # and `cache_control`.
    mime_types {
       css_js {
         mime = "text/css, application/javascript"
         cache_control = "public, max-age=604800, must-revalidate, proxy-revalidate"
       }
    
       images {
         mime = "image/jpeg, image/png, image/gif, image/svg+xml, image/x-icon"
         cache_control = "public, max-age=2628000, must-revalidate, proxy-revalidate"
       }
    }
  }
}

to be released in v0.6.