implement 'downloader' options per extractor category

by setting options inside 'http' or 'ytdl' inside extractor options
or inside subcategory options

{
    "extractor": {
        "mastodon": {
            "http": {
                "rate": "10k"
            }
        },
        "mastodon.social": {
            "http": {
                "rate": "100k"
            }
        }
    },
    "downloader": {
        "rate": "100m"
    }
}

Sets download speed to
-  10k for mastodon.social URLs
- 100k for mastodon sites in general
- 100m for all other sites

test/test_downloader.py

@@ -20,7 +20,6 @@ import tempfile
 import threading
 import http.server
 
-
 sys.path.insert(0, os.path.dirname(os.path.dirname(os.path.abspath(__file__))))
 from gallery_dl import downloader, extractor, output, config, path  # noqa E402
 from gallery_dl.downloader.http import MIME_TYPES, SIGNATURE_CHECKS # noqa E402
@@ -55,6 +54,9 @@ class TestDownloaderModule(unittest.TestCase):
         else:
             del sys.modules["youtube_dl"]
 
+    def setUp(self):
+        downloader._cache.clear()
+
     def tearDown(self):
         downloader._cache.clear()
 
@@ -107,6 +109,63 @@ class TestDownloaderModule(unittest.TestCase):
         self.assertEqual(import_module.call_count, 1)
 
 
+class TestDownloaderConfig(unittest.TestCase):
+
+    def setUp(self):
+        config.clear()
+
+    def tearDown(self):
+        config.clear()
+
+    def test_default_http(self):
+        job = FakeJob()
+        extr = job.extractor
+        dl = downloader.find("http")(job)
+
+        self.assertEqual(dl.adjust_extension, True)
+        self.assertEqual(dl.chunk_size, 32768)
+        self.assertEqual(dl.metadata, None)
+        self.assertEqual(dl.progress, 3.0)
+        self.assertEqual(dl.validate, True)
+        self.assertEqual(dl.headers, None)
+        self.assertEqual(dl.minsize, None)
+        self.assertEqual(dl.maxsize, None)
+        self.assertEqual(dl.mtime, True)
+        self.assertEqual(dl.rate, None)
+        self.assertEqual(dl.part, True)
+        self.assertEqual(dl.partdir, None)
+
+        self.assertIs(dl.interval_429, extr._interval_429)
+        self.assertIs(dl.retry_codes, extr._retry_codes)
+        self.assertIs(dl.retries, extr._retries)
+        self.assertIs(dl.timeout, extr._timeout)
+        self.assertIs(dl.proxies, extr._proxies)
+        self.assertIs(dl.verify, extr._verify)
+
+    def test_config_http(self):
+        config.set((), "rate", 42)
+        config.set((), "mtime", False)
+        config.set((), "headers", {"foo": "bar"})
+        config.set(("downloader",), "retries", -1)
+        config.set(("downloader", "http"), "filesize-min", "10k")
+        config.set(("extractor", "generic"), "verify", False)
+        config.set(("extractor", "generic", "example.org"), "timeout", 10)
+        config.set(("extractor", "generic", "http"), "rate", "1k")
+        config.set(
+            ("extractor", "generic", "example.org", "http"), "headers", {})
+
+        job = FakeJob()
+        dl = downloader.find("http")(job)
+
+        self.assertEqual(dl.headers, {})
+        self.assertEqual(dl.minsize, 10240)
+        self.assertEqual(dl.retries, float("inf"))
+        self.assertEqual(dl.timeout, 10)
+        self.assertEqual(dl.verify, False)
+        self.assertEqual(dl.mtime, False)
+        self.assertEqual(dl.rate, 1024)
+
+
 class TestDownloaderBase(unittest.TestCase):
 
     @classmethod