python,misc: Add check-merge-conflict hook to pre-commit

This hook will check to see if files have merge conflict strings and
blocks commit if so.

Change-Id: I8687e0a8367d3c43133890001023e0352954d90d

.pre-commit-config.yaml

@@ -64,6 +64,7 @@ repos:
             args: [--fix=lf]
           - id: check-ast
           - id: check-case-conflict
+          - id: check-merge-conflict
           - id: requirements-txt-fixer
     - repo: https://github.com/jumanjihouse/pre-commit-hook-yamlfmt
       rev: 0.2.3