Add cleos helper command to add eosio.code to permission

[conr2d]

Change Description

Fixes #6072
This PR adds --add-code and --remove-code options to cleos set account permission command so as to add or remove eosio.code permission conveniently to specified permission authority.

Documentation Additions

Following examples can be added to documentation.

1. Add eosio@eosio.code to eosio@active
cleos set account permission eosio active --add-code

2. Remove eosio@eosio.code from eosio@active
cleos set account permission eosio active --remove-code

3. Add eosio.token@eosio.code to eosio@owner
cleos set account permission eosio owner eosio.token --add-code -p eosio@owner

[arhag]

Nice job. There are three issues I discovered though and I have suggested changes to fix them.

First, it should be possible to add and remove null@eosio.code to an authority. The way you are checking for the null string of the authority to maintain the old behavior of deleting a permission regardless of whether --add-code or --remove-code are specified was preventing that from being possible.

Second, the blockchain rules enforce certain validation rules on authorities provided in updateauth. One of those rules is that the permission_levels specified in the accounts vector of an authority must be in ascending order with no repeats (similar rules apply for keys and waits as well). So, if you just add a new code permission to the end of the accounts vector, it will sometimes fail. My suggested code changes should insert the new code permission into the correct spot.

Third, an authority can consist entirely of waits (meaning no entries in keys and accounts). This is perhaps not a wise move because it means any account can satisfy that authority if they just delay their transaction for long enough. But it is technically a valid authority, and so that must be considered by this cleos command to make sure to not incorrectly delete a permission that won't actually have an empty authority after remove the code permission.

[conr2d]

@arhag I applied all of your suggestions. Thanks for your kind review. :)

[arhag]

Thanks!

For future reference, please just add a new commit of the requested changes rather than force pushing a replacement commit since it makes it easier to review the changes.