docs(ecs): Specify units for DNS TTL (#15656)

Customer reports that it's not clear here what the units of the default "60" are, and furthermore that this appears as "1" (again without units) in the console. Clarify by writing this as `Duration.minutes(1)`


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packages/@aws-cdk/aws-ecs/lib/base/base-service.ts

@@ -945,7 +945,7 @@ export interface CloudMapOptions {
   /**
    * The amount of time that you want DNS resolvers to cache the settings for this record.
    *
-   * @default 60
+   * @default Duration.minutes(1)
    */
   readonly dnsTtl?: Duration;