SONAR-16079: Use `sinceLeakPeriod` in generated hotpots URLs used for PR decoration.

Frontend still recognizes `sinceLeakPeriod` and translates it to `inNewCodePeriod` when it calls the WS.
Therefore, the generated links should still use the old parameter name until the frontend is updated.

SONAR-16079: Update test with 'inNewCodePeriod' parameter
SONAR-16079: Revert usage of "inNewCodePeriod" from the frontend
SONAR-16079: Continue using "sinceLeakPeriod" on the frontend and send the new "inNewCodePeriod" param to the backend
SONAR-16079: Update description for "inNewCodePeriod" parameter
SONAR-16079: Extract static fields for String literals
SONAR-16079: Replace "sinceLeakPeriod" parameter with "inNewCodePeriod" for "api/hotspots/search" internal endpoint