feat(buf.yaml): add protobuf linter config

Change-Id: I0506d0625769caa9f9bcd623722440bebe8b28b5
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1244
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: glittershark <grfn@gws.fyi>

buf.yaml

@@ -0,0 +1,13 @@
+build:
+  roots:
+    #- proto
+    - third_party
+lint:
+  ignore:
+    - nix/buildGo
+  use:
+    - BASIC
+    - FILE_LOWER_SNAKE_CASE
+  except:
+    - ENUM_VALUE_UPPER_SNAKE_CASE
+    - PACKAGE_DIRECTORY_MATCH