Tutorial for builtin-actor development

[BigLep]

Done Criteria

There is a tutorial(s) for doing builtin-actor development and getting those changes into Lotus. Since this focuses on getting changes into Lotus, the docs probably belong in Lotus, and then a pointer to those docs can be in builtin-actors' readme.

Why Important

FilOz wants to empower other people/teams to do this work. One part of doing this is pointing to an example for the steps involved.

User/Customer

New builtin-actor contributors (e.g., new FIP implementers)

Notes

1. There are multiple tiers of change going from easier to harder:
   1. No new method methods
   2. New/changed methods (e.g., serialization change). This involves having corresponding go-state-types change
   3. Change in ref-fvm or proofs
2. In 2024Q3, we expect this to be helpful at the minimum for having others help do https://github.com/filecoin-project/FIPs/pull/1035 and/or https://github.com/filecoin-project/FIPs/discussions/1025