Wizard: Debounce unique validation

Debounce the validation, so we don't validate every character.
Debounce also ensures the right ordering.
Only one request runs at a time, we cancel the previous before we fire a new.

src/constants.ts

@@ -214,6 +214,7 @@ export const EPEL_9_REPO_DEFINITION = {
 };
 
 export const DEBOUNCED_SEARCH_WAIT_TIME = 500;
+export const UNIQUE_VALIDATION_DELAY = 300;
 export const FIRST_BOOT_SERVICE_DATA =
   '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';