Create addExercise hook

Related to https://github.com/garageScript/c0d3-app/issues/1975

Create a query file for [addExercise resolver](https://github.com/garageScript/c0d3-app/blob/5a99b96a5bac6fe0a485d4435f07f2ba522a573f/graphql/resolvers/exerciseCrud.ts#L25).

Example of a query file: [addModule.ts](https://github.com/garageScript/c0d3-app/blob/master/graphql/queries/addModule.ts)