Create `isStudentEnrolled()` function

[aryanprince]

Just a tRPC API endpoint/procedure to check if the given studentId is enrolled or not for a given moduleId.

Takes studentId and moduleId as input, and returns a boolean value ideally.

Open to changes in implementation tho, just an idea ☝️

[lewisj576]

I'd like to do this.

[aryanprince]

@lewisj576 Check updated description now for more info