Add constraint for bugs field in package.json (#1030)

A constraint has been added to ensure that the `bugs` field in
`package.json` is always set to the correct value. This field was not
covered by existing validation.

This constraint is useful for a subsequent PR, where the repository is
renamed.

**Checklist**

- [x] Tests are included if applicable
- [x] Any added code is fully documented

constraints.pro

@@ -155,6 +155,15 @@ gen_enforced_field(WorkspaceCwd, 'repository.type', 'git').
 % packages.
 gen_enforced_field(WorkspaceCwd, 'repository.url', 'https://github.com/MetaMask/controllers.git').
 
+% "bugs.url" must be "https://github.com/MetaMask/controllers/issues" for all
+% workspace packages.
+gen_enforced_field(WorkspaceCwd, 'bugs.url', 'https://github.com/MetaMask/controllers/issues') :-
+  \+ workspace_field(WorkspaceCwd, 'private', true).
+
+% "bugs" must unset for the root.
+gen_enforced_field(WorkspaceCwd, 'bugs', null) :-
+  workspace_field(WorkspaceCwd, 'private', true).
+
 % "license" must be "MIT" for all workspace packages and unset for the root.
 gen_enforced_field(WorkspaceCwd, 'license', 'MIT') :-
   \+ workspace_field(WorkspaceCwd, 'private', true).