change: differentiate two types of candidates in selection process

[AmbientTea]

Description

Introduces separate types for permissioned/trustless candidates so in the future we could preserve that information in committee data on-chain. I think this shouldn't break existing chains but I will need to check that.

UPDATE: Tested this successfully with runtime upgrade on devnet.

Checklist

• Commit sequence broadly makes sense and commits have useful messages.
• New tests are added if needed and existing tests are updated.
• Relevant logging and metrics added
• CI passes. See note on CI.
• Any changes are noted in the changelog.md for affected crate
• Self-reviewed the diff

Note on CI

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