feat: add option skip backpack serializer registration

[johnnyoshika]

Add option to skip backpack serializer registration.

Usage

new Backpack(workspace, {
  skipSerializerRegistration: true,
})

Tests

Tested with the following:

new Backpack(workspace) // Registers serializer

new Backpack(workspace, { skipSerializerRegistration: false}) // Registers serializer

new Backpack(workspace, { skipSerializerRegistration: true }) // Does not register serializer

new Backpack(workspace) // Registers serializer
new Backpack(workspace) // Does not register serializer, as it's already registered
new Backpack(workspace, { skipSerializerRegistration: true }) // Does not register serializer, but it also doesn't unregister serializer

Closes #1826

[maribethb]

Looks great! Thank you for also updating the docs!