CID-3774: Move logic of processing installation event to backend

[mohamedlajmileanix]

🛠 Changes made

Move logic of processing installation event to backend

✨ Type of change

Please delete the options that are not relevant.

• New feature (non-breaking change which adds functionality)

🧪 How Has This Been Tested?

• Updating tests

🏎 Checklist:

• My code follows the style guidelines
• I have performed a self-review of my own code
• Any dependent changes have been merged and published in downstream modules
• My commit message clearly reflects the changes made
• Assigned the appropriate labels (version, PR type, etc.)

[github-actions]

LeanIX GitHub Agent Code Coverage

File	Coverage [67.36%]	🍏
WebhookEventService.kt	100%	🍏
InstallationRequestDTO.kt	83.33%	🍏
InstallationGetHandler.kt	45.81%	❌
BrokerStompSessionHandler.kt	21.01%	❌

Total Project Coverage	65.5%	🍏