fix: show warning for non-existent cost meter metrics

[namanv3]

Pull Request

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If an organisation hasn't set up cost meters, then the costs page currently throws errors for them. Given that these are internal metrics, we should not do this. We should just give a warning.

Screenshots / Screen Recordings (if applicable)

Issues closed by this PR

Closes https://github.com/SigNoz/engineering-pod/issues/4325

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✅ Change Type

Select all that apply

• ✨ Feature
• 🐛 Bug fix
• ♻️ Refactor
• 🛠️ Infra / Tooling
• 🧪 Test-only

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🐛 Bug Context

What the meters page looked like before #10560

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🧪 Testing Strategy

How was this change validated?

• Tests added/updated: Integration tests
• Manual verification: Done, screenshots added
• Edge cases covered: Yes

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📝 Changelog

Fill only if this affects users, APIs, UI, or documented behavior
Use N/A for internal or non-user-facing changes

Field	Value
Deployment Type	Cloud / OSS / Enterprise
Change Type	Bug Fix
Description	If cost meters have not been set, the page does not throw errors anymore

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📋 Checklist

• Tests added or explicitly not required
• Manually tested
• Breaking changes documented
• Backward compatibility considered

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