feat: add Kapacitor provider

[janisag07]

Summary

Adds a new Kapacitor provider to receive time-series alerts from InfluxData's Kapacitor.

Changes

• keep/providers/kapacitor_provider/kapacitor_provider.py — Full provider implementation
• keep/providers/kapacitor_provider/alerts_mock.py — Sample TICKscript alerts (CPU, disk, service recovery)
• tests/test_kapacitor_provider.py — Unit tests for all alert levels

Features

• Webhook ingestion: Receives TICKscript HTTP POST alerts (JSON format)
• API pull: Queries alerts via /kapacitor/v1/alerts/topics endpoint
• Level mapping: CRITICAL→critical/firing, WARNING→warning/firing, INFO→info/firing, OK→low/resolved
• Authentication: Optional HTTP Basic Auth (username/password)
• PROVIDER_TAGS, PROVIDER_SCOPES, FINGERPRINT_FIELDS configured

Linked Issue

Closes #4754

Use Cases

• Complex time-series alerts from InfluxDB data
• TICKscript-based monitoring integration
• Real-time data stream alerting

Benefits over direct PagerDuty

• Alert correlation and enrichment in Keep
• Side-loading context data before escalation
• Better alert routing and noise reduction

Checklist

• Provider follows existing patterns
• Unit tests for all alert levels
• CODE-DOC-TEMPLATE.md included
• HTTP Basic Auth implemented

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[janisag07]

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[janisag07]

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