ci: Disable mergify on draft PRs

Disable automerge if PR is draft or has DNM label

Signed-off-by: Jan Gałda <jan.galda@nordicsemi.no>

Author: jangalda-nsc

.github/mergify.yml

@@ -4,6 +4,8 @@ pull_request_rules:
       - base=main
       - "#approved-reviews-by>=1"
       - approved-reviews-by=@ncs-code-owners
+      - -draft
+      - -label=DNM
       - or:
         - label=manifest-homekit
         - label=manifest-find-my