fix: Simpler approach to load all incident params into labels

[Jleee713]

📑 Description

closes #6542

Fix _format_alert in the Site24x7 provider so that webhook incident parameters are correctly surfaced as alert labels.

Previously the code looked for a LABELS key in the webhook payload (event.get("LABELS", "")), which Site24x7 never sends. Incident parameters ($STATUS, $MONITORTYPE, $INCIDENT_DETAILS, $FAILED_LOCATIONS, etc.) are delivered as top-level fields in the JSON body, so labels was always empty.

Change: replace the dead LABELS key lookup with a dict comprehension over all top-level event fields, so every incident parameter sent by Site24x7 is captured in labels.

Labels now populated from Site24x7 incident parameters on monitor DOWN/TROUBLE/CRITICAL/UP events
No manual field exclusion list — simpler and maintenance-free
Existing AlertDto fields (name, url, description, etc.) unchanged
✅ 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
Before (labels always empty):

labels_raw = event.get("LABELS", "") # Site24x7 never sends this key
...
labels = {}
After (labels populated from all incident parameters):

labels = {k: str(v) for k, v in event.items() if v is not None}

[shahargl]

For backward compatibility, keep the original logic and just add the latter (instead of removing), unless you have a very good reason why the old logic is not needed

[Jleee713]

The original logic only works if user configures custom labels parameters in Site24x7 for each monitor. The only use-case for that is if user does not want all incident parameters in webhook, however we can just pass all incident parameters with option to filter on keephq side.

Either way, this automatically populates the incident parameters in labels without repeated configuration from site24x7.

[shahargl]

@Jleee713 but isn't Site24x7 is doing that with setup_webhook, so whoever installs it via setup webhook won't have labels now?