Fix unreadable Grant instruction validator error message

[Arjentix]

Problem

Take a look at default_permissions() at permissions_validators/src/public_blockchain/mod.rs. This configuration is used for checking instrucitons in Iroha 2 by default right now.

The first part of validators configuration is called grant_instruction_validator. If this part fails then it produces error message that says pretty nothing:

Error: Transaction was rejected

Caused by:
   0: Transaction rejected due to insufficient authorisation
   1: Action not permitted: None of the instructions succeeded in Any permission check block with name: Grant instruction validator.

All we can retrieve from this message is that something is wrong with some Grant instruction. We don't know which instruction and what is exactly wrong.
That was a problem while debugging #2081

Suggested solution

I, personally, think that using Result doesn't fit well for validators, because we can't tell what (Err or Ok) should be returned from validator if it gets unexpected instruction. Right now Grant validators return Err, but Instruction validators return Ok. We need a unified way to do it. We need 3 variants: Ok, Err and Skip. We could use Option<Result<...>> but it looks ugly in my opinion.

So my suggestions is to introduce another return type for validators and refactor complex validators construction. This will allow us to tell which validators have failed in any_should_succeed() and etc. Altough I think that any_should_succeed() and all_should_succeed() will be less usable then and we can introduce noone_should_fail() which would meen "All should return Skip or Ok". And maybe at_least_one_success()

[Arjentix]

Yes, something like:

enum ValidatorVerdict {
    Allow,
    Deny(DenialReason),
    Skip,
}

[Arjentix]

Our validation scheme reminds me about chain-of-responsibility pattern