[CORL-409] Prevent users from ignoring staff members (#2355)

* Throw error if user tries to ignore a staff member

Throws a UserCannotBeIgnoredError if a user tries to ignore
a user who is a staff member. A staff member in this case is
considered anyone who has a role of staff, moderator, or admin.

CORL-409

* Prevent users from ignoring staff in the user info popover

Creates the staff roles in a constant next to the user model.
Uses this to add a computed property to the user resolver.

CORL-409

* Remove unnecessary async declaration from userIsStaff helper function

CORL-409

* Specify ignoreable on users in client test fixtures

Allows the tests to pass for the required computed property
of ignoreable that is computed by whether a user is a staff
member or not.

CORL-409

* Update more fixtures with ignoreable property on mocked users/commenters

CORL-409

* Consolidate ignore-able calculation into re-usable helper methods

Re-use the logic for whether a role is a staff member to
clearly define when a user is ignore-able or not across the
business logic.

CORL-409

* Set the ignoreable optimisticResponse on comment mutations

We have set the ignoreable value in the graphQL schema, so now
the optimisticResponses are looking for a default value to use
until the data result arrives. Put to false since the ignoreable
value is set on our author, we likely don't want to ignore ourselves.

CORL-409

src/core/client/admin/test/fixtures.ts

@@ -289,6 +289,7 @@ export const users = {
         username: "Markus",
         email: "markus@test.com",
         role: GQLUSER_ROLE.ADMIN,
+        ignoreable: false,
       },
     ],
     baseUser
@@ -300,6 +301,7 @@ export const users = {
         username: "Lukas",
         email: "lukas@test.com",
         role: GQLUSER_ROLE.MODERATOR,
+        ignoreable: false,
       },
     ],
     baseUser
@@ -311,6 +313,7 @@ export const users = {
         username: "Huy",
         email: "huy@test.com",
         role: GQLUSER_ROLE.STAFF,
+        ignoreable: false,
       },
     ],
     baseUser
@@ -322,18 +325,21 @@ export const users = {
         username: "Isabelle",
         email: "isabelle@test.com",
         role: GQLUSER_ROLE.COMMENTER,
+        ignoreable: true,
       },
       {
         id: "user-commenter-1",
         username: "Ngoc",
         email: "ngoc@test.com",
         role: GQLUSER_ROLE.COMMENTER,
+        ignoreable: true,
       },
       {
         id: "user-commenter-2",
         username: "Max",
         email: "max@test.com",
         role: GQLUSER_ROLE.COMMENTER,
+        ignoreable: true,
       },
     ],
     baseUser
@@ -344,6 +350,7 @@ export const users = {
       username: "Ingrid",
       email: "ingrid@test.com",
       role: GQLUSER_ROLE.COMMENTER,
+      ignoreable: true,
       status: {
         current: [GQLUSER_STATUS.BANNED],
         ban: { active: true },