Move flake8 as a pre-commit local target.

The goal here is to avoid conflicts between flake8 and hacking version each
2 days.

Inspired from nova's approach [1].

The flake8 version to install will be determined by hacking and
requirements will stay aligned instead of relying on different versions.

[1] https://opendev.org/openstack/nova/src/branch/master/.pre-commit-config.yaml#L26-L35
[2] https://opendev.org/openstack/hacking/src/branch/master/requirements.txt#L1

Change-Id: I9a16d80f361f223c4c5c8cdcf90e920abd89f679

.pre-commit-config.yaml

@@ -27,9 +27,13 @@ repos:
       - id: debug-statements
       - id: check-yaml
         files: .*\.(yaml|yml)$
-  - repo: https://gitlab.com/pycqa/flake8
-    rev: 181bb46098dddf7e2d45319ea654b4b4d58c2840 # 3.8.3
+  - repo: local
     hooks:
       - id: flake8
+        name: flake8
         additional_dependencies:
           - hacking>=3.0.1,<3.1.0
+        language: python
+        entry: flake8
+        files: '^.*\.py$'
+        exclude: '^(doc|releasenotes|tools)/.*$'