[PM-6818] legacy generator service adapter (#8582)

* introduce legacy generators
* introduce generator navigation service
* Introduce default options. These accept a userId so that they can be policy-defined
* replace `GeneratorOptions` with backwards compatible `GeneratorNavigation`

libs/common/src/tools/generator/abstractions/generator.service.abstraction.ts

@@ -21,6 +21,9 @@ export abstract class GeneratorService<Options, Policy> {
    */
   evaluator$: (userId: UserId) => Observable<PolicyEvaluator<Policy, Options>>;
 
+  /** Gets the default options. */
+  defaults$: (userId: UserId) => Observable<Options>;
+
   /** Enforces the policy on the given options
    * @param userId: Identifies the user making the request
    * @param options the options to enforce the policy on