write an RFC for graph deprecation schema/validation

[grokspawn]

Write an RFC based on brief to develop a shared design intent on graph deprecation

Acceptance Criteria

• satisfies functional requirements of brief
• documents interface/UX changes
• identifies documentation impacts
• is reviewed and approved

[grokspawn]

Doc here

Implementation areas

1. schema def, parsing (alpha/declcfg/declcfg.go, utests)
2. validation command update (alpha/model/model.go, utests) (killed this since validation will be handled as part of model conversion for GRPC API updates)
3. visualization update (cmd/opm/alpha/render-graph/cmd.go..., utests)
4. GRPC API (pkg/registry/types.go, utests)
5. migrate command update (not clear if we need this) <-- we could implement later to service migration from sqlite catalog formats (olm.deprecated & olm.substitutesfor) (killed this since the previous expression of 'deprecated' meant 'uninstallable' and there's not enough strong inference to convert to the new meaning)

[grokspawn]

Matured by consensus date