Closes #3810

📑 Description

Adds new Icinga2 Provider for Integration with Icinga2 Monitoring System. Implementation Entails:-

• Basic auth with Icinga2 API
• Alert fetch and mapping to Keep alert format
• Icinga2 states mapping to Keep alert severities.
• Alert acknowledgment and removal
• Scope validations for r/w permissions

✅ Checks

• My pull request adheres to the code style of this project
• My code requires changes to the documentation
• I have updated the documentation as required
• All the tests have passed

ℹ Additional Information

• Follows [BaseProvider]
• Uses requests session for connection pooling.
• SSL verification config.
• Alert Ids are of format {hostname}_{servicename}

/claim #3810