tools: Add tool's versions update with checksum file

'idf_tools.py add-version' has new options:
--override            Override tool versions with new data
--checksum-file       URL or path to local file with checksum/size for artifacts

Usage e.g.:
CHECKSUM_URL=https://github.com/espressif/crosstool-NG/releases/download/esp-2021r2/crosstool-NG-esp-2021r2-checksum.sha256
idf_tools.py add-version --tool xtensa-esp32-elf --version esp-2021r2 --override --checksum-file $CHECKSUM_URL

Positional argument 'files' moved to optional argument '--artifact-file'

Add tests for add-version logic

tools/test_idf_tools/add_version/artifact_input.json

@@ -0,0 +1,12 @@
+[
+        {
+            "filename": "xtensa-esp32-elf-test-linux-amd64.tar.gz",
+            "size": 10,
+            "sha256": "d2d02ea74de2c9fab1d802db969c18d409a8663a9697977bb1c98ccdd9de4372"
+        },
+        {
+            "filename": "xtensa-esp32-elf-test-linux-armhf.tar.gz",
+            "size": 20,
+            "sha256": "d1b3707fbdc6a22d16e95bf6b910646f5d9c2b3ed81bd637d454ffb9bb0948e4"
+        }
+]