Make flake8 to be more opinionated (#217)

Currently it is spitting out too many failures.

It is consistent with ExecuTorch linter

.flake8

@@ -0,0 +1,76 @@
+[flake8]
+select = B,C,E,F,P,W,B9,TOR0,TOR1,TOR2
+max-line-length = 120
+ignore =
+    # Black conflicts and overlaps.
+    B950,
+    E111,
+    E115,
+    E117,
+    E121,
+    E122,
+    E123,
+    E124,
+    E125,
+    E126,
+    E127,
+    E128,
+    E129,
+    E131,
+    E201,
+    E202,
+    E203,
+    E221,
+    E222,
+    E225,
+    E226,
+    E227,
+    E231,
+    E241,
+    E251,
+    E252,
+    E261,
+    E262,
+    E265,
+    E271,
+    E272,
+    E301,
+    E302,
+    E303,
+    E305,
+    E306,
+    E501,
+    E502,
+    E701,
+    E702,
+    E703,
+    E704,
+    W291,
+    W292,
+    W293,
+    W391,
+    W504,
+
+    # Too opinionated.
+    E265,
+    E266,
+    E402,
+    E722,
+    B001,
+    P207,
+    B003,
+    P208,
+    C403,
+    W503,
+
+    # Bugbear has opinions: https://github.com/PyCQA/flake8-bugbear#opinionated-warnings
+    B904,
+    B905,
+    B906,
+    B907,
+exclude =
+    ./.git,
+    *.pyi
+
+max-complexity = 12
+