suggest an option for splitting specified files

[hyuraku]

Subject of the issue

RSpec: Is there an option in RSpec to split specified files similar to Jest's shard option? https://github.com/jestjs/jest/pull/12546

Your environment

• Ruby version:
• rspec-core version:

Steps to reproduce

Expected behavior

Actual behavior

[pirj]

There are several methods for parallelization.