[Fix] Fix and divide request(endpoint:) when firestoreMethod type is update,save,delete

• In previous code, FirestoreService.requet(endpoint:) -> AnyPublihser<Void, FirestoreServiceError>'s save, update logic was equal using firestore's setData func. But It isn't good as it may overwrite previously existing fields in a document.

• So I replaced setData with updateData func and addDocument func when FirestoreMehtod types is update or save.

Improved FirestoreService query function

• Improvement of overlapping Firestore query parameters.
• Firestore Service Protocol return type Error -> Abstract to FirestoreService Error -> Concrete conversion

A simple example to utilize SHFirestoreService has been added.

In the example, you can see the logic of making a request to Firestore and receiving a response through the FirestoreService object based on the endpoint and request type.

[Fix] FirestoreService's init access modifier convert to public

FirestoreService's init access modifier converted to public.

First Release SwiftPM

SHFirestoreService implementation.

The example has not been implemented yet.