fix(ui-devkit): Silence sass warnings during compilation

A transitive dependency bump caused many sass warnings to show up
during compilation. Using this feature to silence: https://github.com/angular/angular-cli/pull/28627

packages/admin-ui/angular.json

@@ -40,7 +40,10 @@
               "includePaths": [
                 "./src/lib/static/styles",
                 "./src/lib/static/fonts"
-              ]
+              ],
+              "sass": {
+                "silenceDeprecations": ["mixed-decls", "color-functions", "global-builtin", "import"]
+              }
             },
             "allowedCommonJsDependencies": [
               "graphql-tag",

packages/ui-devkit/scaffold/angular.json

@@ -55,7 +55,10 @@
               "includePaths": [
                 "./src/styles",
                 "./src/fonts"
-              ]
+              ],
+              "sass": {
+                "silenceDeprecations": ["mixed-decls", "color-functions", "global-builtin", "import"]
+              }
             },
             "allowedCommonJsDependencies": [
               "graphql-tag",