Hot Fix: inconsistency of changes since last merge conflicts resolution

Overview

This pull request fixes some errors in the name of methods used in the subjects service and updated the Get route in the subjects controller.

Method: Updated find() to use query params and custom instances of ParseIntPipe to validate the datatype of query params
Hot Fix: Wrong methods names replaced
Route: Added missing delete handler in controller
Route

Added route handler for http delete requests, this feature was missing, the method for delete was avaliable in the service but no method for delete was present in the controller, it seems like at some point, the route was removed in the last merge conflict resolution.
delete() now avaliable in subject.controller.ts

Some changes were lost in the last merge conflict resolution Example of the inconsistency showed in the code base:

<<<<<<< feature/subjects
    if (await this.foreign.validate())
=======
    if (await this.foreign.validateError())
>>>>>>> dev

Notice that this.foreign.validateError() doesn't exist and is currently in the dev branch

Right now, the merge conflicts are resolved, only need a check to be sure of what changes are being accepted

Note: the second statement was a non-updated change but it was merged together with the other changes