Introduce a CI job that validates RFCs

We can start with a simple lint check like the one we run in https://github.com/FuelLabs/fuel-specs and we can expand to something more substantial like https://github.com/ethereum/eip_validator

Start by reviewing the lint check used in the referenced Fuel specs repository and the ethereum/eip_validator project. Define the validation scope for this RFC repository, then confirm that the CI job detects invalid RFCs and passes for valid ones.

Written by the indexing model from the issue text.