[codespell] fix final typos and enable ci

This chnage adds the pre-commit config and
tox targets to run codespell both indepenetly
and via the pep8 target.

This change correct all the final typos in the
codebase as detected by codespell.

Change-Id: Ic4fb5b3a5559bc3c43aca0a39edc0885da58eaa2

.pre-commit-config.yaml

@@ -34,3 +34,8 @@ repos:
     hooks:
       - id: autopep8
         files: '^.*\.py$'
+  - repo: https://github.com/codespell-project/codespell
+    rev: v2.2.4
+    hooks:
+    - id: codespell
+      args: ['--ignore-words=doc/dictionary.txt']