fix: add " to the new update_interval_* options of the autoscaler (#1177)

## Description

The new options `update_interval` and `update_interval_when_expecting`
are strings and need a `"` around the value. Otherwise the configuration
file has the wrong format and the Agent might not work as expected.

Closes #1176

Author: kayman-mk

template/runner-docker-autoscaler-config.tftpl

@@ -3,8 +3,8 @@
     plugin = "fleeting-plugin-aws"
 
     capacity_per_instance = ${runners_capacity_per_instance}
-    update_interval = ${runners_update_interval}
-    update_interval_when_expecting = ${runners_update_interval_when_expecting}
+    update_interval = "${runners_update_interval}"
+    update_interval_when_expecting = "${runners_update_interval_when_expecting}"
 
     max_use_count = ${runners_max_use_count}
     max_instances = ${runners_max_instances}