lint: isort pre-commit & misc improvements (#3749)

* test: clean flake8 config root clutter

* test: pre-commit: add isort

Compatible with black (see https://github.com/timothycrosley/isort/issues/694)

* lint: reorder imports

* lint: more complex imports

* lint: fix deepsource

* config: isort: add first party dvc

* tests: restyled: add isort

* temp commit to revert before merge

* Revert "temp commit to revert before merge"

This reverts commit 11db0fd8e95fe891597cbb9bf804480909b19e24.

tests/unit/test_analytics.py

@@ -1,9 +1,9 @@
-import pytest
-import mock
-import platform
 import json
+import platform
 
-from voluptuous import Schema, Any
+import mock
+import pytest
+from voluptuous import Any, Schema
 
 from dvc import analytics
 from dvc.cli import parse_args