feat: Add Cheatcodes::AddAccount

[jbargu]

Give an overview of the tasks completed
Arbiter currently assumes all accounts are initialized before the execution. However sometimes the user cannot anticipate all the involved accounts. With the Cheatcodes::AddAccount cheat code, the user can inject a new account mid execution and then update the balance with Cheatcodes::Deal cheat code.

The PR is based on top of #977.

REMINDER! Please check that you have done the following prior to submitting this PR:

• Checked that the relevant version(s) have been incremented if necessary.
• Ran both and made any changes necessary for:
  • cargo +nightly fmt --all
  • cargo clippy --all

[Alexangelj]

Reviewing next week

[Alexangelj]

Overall like the changes - just need to make sure everything merges in clean

[jbargu]

At first I wanted to expose the whole Instruction struct and add Cheatcodes(Instruction) but then the struct is cyclic.

Maybe a more sound way would be to have an apply_instruction(Instruction) function or modify apply_cheatcode(Cheatcodes) to apply_cheatcode(Instruction) however this would be a breaking change.

[Alexangelj]

Actually - maybe we can just keep the existing apply_cheatcode and expose a new method apply_instruction(Instruction), @kinrezC wdyt?