twister: Add support for required snippets

Adds support for twister to require using snippets on tests

Signed-off-by: Jamie McCrae <jamie.mccrae@nordicsemi.no>

scripts/schemas/twister/testsuite-schema.yaml

@@ -145,6 +145,11 @@ mapping:
         matching: "all"
         sequence:
           - type: str
+      "required_snippets":
+        type: seq
+        required: false
+        sequence:
+          - type: str
       "tags":
         type: any
         required: false
@@ -243,6 +248,11 @@ mapping:
           "extra_sections":
             type: any
             required: false
+          "required_snippets":
+            type: seq
+            required: false
+            sequence:
+              - type: str
           "filter":
             type: str
             required: false