Fix snap grade (#598)

Cherry-pick 604f83f.

In the release branch, where the grade logic resolves to "stable", the build failed. Adding the `adopt-info` key in snapcraft.yaml fixed the issue. In the main branch, grade should always resolve to "devel", which doesn't have this problem. But I'm cherry-picking the change from the release branch anyway for consistency.

snap/snapcraft.yaml

@@ -10,6 +10,7 @@ description: |
 license: MIT 
 
 confinement: strict
+adopt-info: iot-identity-services
 
 parts:
   rust-toolchain: