chore(lint): Enable localmodule for import linter (#1989)

We use three sections through-out the codebase -- standard, default, and
localmodule.  This change updates the linter to enforce this pattern as
files are added or modified.

.golangci.yml

@@ -95,6 +95,7 @@ linters-settings:
     sections: # defines the order of import sections
       - standard
       - default
+      - localmodule
   goconst:
     min-len: 3 # min length for string constants to be checked
     min-occurrences: 3 # min occurrences of the same constant before it's flagged