Add validation service settings by provided schema ability.

[wiva-koikoi]

📝 Description

Add new setting "$validationSchema" and validation step.
With it (if broker.validator is defined) we can validate service settings object after merged() (means after merging all mixins with own settings) but before created() calls.

🎯 Relevant issues

💎 Type of change

• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

📜 Example code

import { ValidationSchema } from "fastest-validator";

const $validationSchema: ValidationSchema = {
  $$strict: false,

  batchSize: { integer: true, positive: true, type: "number" },
};


const serviceSchema: ServiceSchema = {
    settings: {
        $validationSchema,

        // throws ValidationError, because batchSize setting expects number.
        batchSize: "10",
    },
};

🏁 Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• I have commented my code, particularly in hard-to-understand areas

[icebob]

Nice, but while it doesn't affect the core logic, it can be a nice external middleware (using the serviceCreating hook). So please create a separate repo under your account and publish it as middleware and send us to the awesome-moleculer repo.