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/func/test_plot.py

@@ -6,21 +6,21 @@ from collections import OrderedDict
 
 import pytest
 import yaml
-from bs4 import BeautifulSoup
 from funcy import first
 
+from bs4 import BeautifulSoup
 from dvc.compat import fspath
+from dvc.repo.plot import NoDataOrTemplateProvided
 from dvc.repo.plot.data import (
     NoMetricInHistoryError,
-    PlotMetricTypeError,
     PlotData,
+    PlotMetricTypeError,
 )
 from dvc.repo.plot.template import (
-    TemplateNotFoundError,
     NoDataForTemplateError,
     NoFieldInDataError,
+    TemplateNotFoundError,
 )
-from dvc.repo.plot import NoDataOrTemplateProvided
 
 
 def _remove_whitespace(value):