mooclet backend: refactor the redundant mooclet.enabled checks

[danoswaltCL]

We have several places now where we are checking if the experiment has a mooclet assignment algorithm and/or moocletPolicyParameters but mooclet is not enabled to throw an error. This sort of thing:

if (SUPPORTED_MOOCLET_ALGORITHMS.includes(experiment.assignmentAlgorithm)) {
      if (!env.mooclets?.enabled) {

We can refactor to create a utility function to reduce duplicate logic.

Requirements:

• Create a utility function on MoocletExperimentService to perform this check and throw an error if the entity we are using deals with mooclet resources without mooclet being enabled.