Unify FGA Model parsing and validation

[aaguiarz]

Currently we have different implementations for validating FGA models (JS/Go/Java implementations in openfga/language and in the OpenFGA server).

The goal is:

• Keep validation in the Go implementation
• Create a LSP through the CLI so we can use it for IDE integrations
• Possibly a WASM output for browser support

[ErlingWis]

Hello! Is exposing validation functionality in a go package part of this, or is the plan to keep this functionality internally in the cli?

We would love to have validation and testing available as packages to support deploying fga modules with tests to kubernetes and have an operator performing validation and testing to ensure modules don't break the compiled model. We're able to do this today by running the cli in a container and parsing the results, but having access to the functionality directly as functions would eliminate some moving parts :)