fix(request): Properly declare optional request parameters

Optional is not the right way to declare that a particular request
parameter is not required. There was a similar issue in the corresponding
clouddriver endpoint that was fixed by
spinnaker/clouddriver#6067

gate-web/src/main/groovy/com/netflix/spinnaker/gate/controllers/CredentialsController.groovy

@@ -97,11 +97,11 @@ class CredentialsController {
     @ApiParam(value = 'Value of the "@type" key for accounts to search for.', example = 'kubernetes')
     @PathVariable String accountType,
     @ApiParam('Maximum number of entries to return in results. Used for pagination.')
-    @RequestParam OptionalInt limit,
+    @RequestParam(required = false, defaultValue = "100") Integer limit,
     @ApiParam('Account name to start account definition listing from. Used for pagination.')
-    @RequestParam Optional<String> startingAccountName
+    @RequestParam(required = false) String startingAccountName
   ) {
-    clouddriverService.getAccountDefinitionsByType(accountType, limit.isPresent() ? limit.getAsInt() : null, startingAccountName.orElse(null))
+    clouddriverService.getAccountDefinitionsByType(accountType, limit, startingAccountName)
   }
 
   @PostMapping