chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/configuration/settings/publicip_test.go

@@ -15,7 +15,6 @@ func Test_PublicIP_read(t *testing.T) {
 		makeReader func(ctrl *gomock.Controller) *reader.Reader
 		makeWarner func(ctrl *gomock.Controller) Warner
 		settings   PublicIP
-		errWrapped error
 		errMessage string
 	}{
 		"nothing_read": {
@@ -152,9 +151,10 @@ func Test_PublicIP_read(t *testing.T) {
 			err := settings.read(reader, warner)
 
 			assert.Equal(t, testCase.settings, settings)
-			assert.ErrorIs(t, err, testCase.errWrapped)
-			if testCase.errWrapped != nil {
+			if testCase.errMessage != "" {
 				assert.EqualError(t, err, testCase.errMessage)
+			} else {
+				assert.NoError(t, err)
 			}
 		})
 	}