feat: add Coroot monitoring provider

[janisag07]

Summary

Adds a new Coroot provider to receive monitoring alerts via webhooks and query the Coroot API.

Changes

• keep/providers/coroot_provider/coroot_provider.py — Full provider implementation
• keep/providers/coroot_provider/alerts_mock.py — Sample webhook payload
• tests/test_coroot_provider.py — 5 unit tests

Features

• Webhook ingestion: Receives alerts when Coroot detects incidents (CRITICAL, WARNING, OK)
• API query: Fetches application list via /api/v1/applications
• Status→Severity mapping: CRITICAL→critical, WARNING→warning, OK→info/resolved
• PROVIDER_TAGS, PROVIDER_SCOPES, FINGERPRINT_FIELDS configured

Linked Issue

Closes #5412

Checklist

• Provider follows existing patterns (auth config, webhook markdown, format_alert)
• Unit tests pass
• alerts_mock.py with realistic payload
• CODE-DOC-TEMPLATE.md included

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[janisag07]

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[janisag07]

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