Remote notifications methods do not throw if no default implementation

[marandaneto]

What does this PR do?

Add default implementation for remote notifications methods

Where should the reviewer start?

How should this be manually tested?

Tested by calling methods manually

What are the relevant tickets?

Closes https://github.com/PostHog/posthog-ios/issues/70

Screenshots or screencasts (if UI/UX change)

Questions:

• Does the docs need an update?
• Are there any security concerns?
• Do we need to update engineering / success?