[Utility] Client should validate relay contents

[adshmh]

Objective

Relay contents should be validated on client-side before being sent to the target (e.g. a servicer in case of trustless relays)

Origin Document

Client should not be sending relays with a clearly invalid contents, e.g. missing jsonrpc string in case of JSONRPC relays.
But this is not currently done:

Goals

• Discuss the validations. More specifically:
  - Should the client perform validations specific to the target relay chain (e.g. not allow JSONRPC if the relay chain expects RESTful relays)
  - Should the client use or at-least enable the addition of method/chain-specific content validators: e.g. a custom/buildin validator that ensures the params object is valid for the specified method.
• Perform "basic" relay content validation, whatever the definition of "basic" ends up to be for now.

Deliverable

• MVP validation code for relay contents: limit the scope to JSONRPC and RESTful relays
• Updated documentation as this is a user-facing change.
• one or more issues that describe additional builtin/custom relay validators

Non-goals / Non-deliverables

• Perform a complete validation of any of the relay types, e.g. JSONRPC, and guarantee correctness

General issue deliverables

• Update any relevant local/global README(s)
• Update relevant source code tree explanations
• Add or update any relevant or supporting mermaid diagrams

Testing Methodology

• Task specific tests or benchmarks: make ...
• New tests or benchmarks: make ...
• All tests: make test_all
• LocalNet: verify a LocalNet is still functioning correctly by following the instructions at docs/development/README.md
• k8s LocalNet: verify a k8s LocalNet is still functioning correctly by following the instructions here

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Creator: [@adshmh ]
Co-Owners: [@Olshansk]