feat(frontend): show performance milestone attestation status on schedule detail page

[libby-coder]

Problem

When a schedule has requires_milestones = true, beneficiaries cannot see the attestation status from the UI. They don't know whether their milestones have been attested by the oracle, so they don't know whether a claim will succeed.

What to add

On the schedule detail page, when requires_milestones is true, fetch get_milestones(schedule_id) and render each milestone with its attested/pending status and attested timestamp.

[Songu3020]

@Songu3020 has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

Hi, I'm Peter — a Full-Stack & Blockchain Developer with 3+ years of experience. I've reviewed this issue and I'm confident I can handle it. I'll submit a clean PR within 1-2 days max. Please assign it to me!

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[superstarflayce]

@superstarflayce has applied to work on this issue as part of the Stellar Wave Program's 6th wave.

I would like to work on this project

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[drips-wave]

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