Support Modular Models

[rhamzeh]

Intro

Roadmap Item: https://github.com/openfga/roadmap/issues/39 Modular Models RFC

Sub-tickets

• [x] #149
• [x] #150
• [x] #151
• [x] #152
• [x] #153
• [x] #154
• [x] #180
• [x] #186
• [x] #187
• [x] #199

For this epic, we're going to have a long running feature branch feat/148-support-modular-models that will have all our changes to support this feature

Related tickets

• https://github.com/openfga/api/issues/137 (blocker)
• https://github.com/openfga/vscode-ext/issues/165
• https://github.com/openfga/cli/issues/262
• https://github.com/openfga/openfga/issues/1402