Remove Default impl for Credentials

[ilslv]

Synopsis

Remove Default impl for Credentials, as it's not deterministic and may be a foot gun because of that.

Checklist

• Created PR:
  • [x] In draft mode
  • [x] Name contains Draft: prefix
  • [x] Name contains issue reference
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• [x] Documentation is updated (if required)
• [x] Tests are updated (if required)
• [x] Changes conform code style
• [x] CHANGELOG entry is added (if required)
• [x] FCM (final commit message) is posted
  • [x] and approved
• [x] Review is completed and changes are approved
• Before merge:
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[ilslv]

FCM

Remove `Default` impl for `member::Credentials` in Control API protocol (#63)