feat: multi-actor config

[krpeacock]

Description

As requested, allows the useAuthClient hook to create and manage multiple actors at once. I don't know how to infer the full typing, but that may be possible in a future version

Also adds example code for initializing multiple actors

How Has This Been Tested?

new unit test and refactoring in the example app

Checklist:

• My changes follow the guidelines in CONTRIBUTING.md.
• The title of this PR complies with Conventional Commits.
• I have edited the CHANGELOG accordingly.
• I have made corresponding changes to the documentation.

[github-actions]

size-limit report 📦

Path	Size
@dfinity/agent	85.96 KB (0%)
@dfinity/candid	13.58 KB (0%)
@dfinity/principal	4.97 KB (0%)
@dfinity/auth-client	60.36 KB (0%)
@dfinity/assets	80.98 KB (0%)
@dfinity/identity	57.56 KB (0%)
@dfinity/identity-secp256k1	131.14 KB (0%)