Add persist form functionality

[NetanelBasal]

It'll be great to add a built-in method to persist the form value to the storage. For example:

const profileForm = new FormGroup<Profile>({
  firstName: new FormControl(''),
  lastName: new FormControl(''),
  skills: new FormArray([]),
  address: new FormGroup({
    street: new FormControl(''),
    city: new FormControl('')
  })
});

profileForm.persist(key, storage);

Where the key is the storage key, and the storage is local or session.

[caroso1222]

I wonder if you'd like to follow a more functional approach for the API on this one. Something along the lines of

import { LocalStorageManager } from '@ngneat/reactive-forms';

const profileForm = new FormGroup<Profile>({
  firstName: new FormControl(''),
  lastName: new FormControl(''),
});

LocalStorageManager.serialize(key, profileForm)
LocalStorageManager.deserialize(key)

It would allow the feature to scale with more managers like SessionStorageManager, IndexedDBManager, all of them implementing a common IPersistManager interface.

Not sure about this claim, but I suppose this could be easier to tree shake rather than having a persist method with a switch-case statement for local, session, etc.

I don't have any problem with .persist, though. Just picking brains on this one.

[NetanelBasal]

We can combine the ideas and create something like:

profileForm.persist(key: string, storage: IPersistManager)

I think we still need to provide at least the default behavior and save it to localstorage if storage isn't provided.