Add CSV to Markdown table conversion - fixes #1144 (#1176)

* feat: Add CSV to Markdown table converter

- Add new CsvConverter class to convert CSV files to Markdown tables\n- Support text/csv and application/csv MIME types\n- Preserve table structure with headers and data rows\n- Handle edge cases like empty cells and mismatched columns\n- Fix Azure Document Intelligence dependency handling\n- Register CsvConverter in MarkItDown class

----

Thanks also to @benny123tw who submitted a very similar PR in #1171

packages/markitdown/tests/_test_vectors.py

@@ -144,10 +144,11 @@ GENERAL_TEST_VECTORS = [
         charset="cp932",
         url=None,
         must_include=[
-            "名前,年齢,住所",
-            "佐藤太郎,30,東京",
-            "三木英子,25,大阪",
-            "髙橋淳,35,名古屋",
+            "| 名前 | 年齢 | 住所 |",
+            "| --- | --- | --- |",
+            "| 佐藤太郎 | 30 | 東京 |",
+            "| 三木英子 | 25 | 大阪 |",
+            "| 髙橋淳 | 35 | 名古屋 |",
         ],
         must_not_include=[],
     ),