feat: add progressive @override support with label argument

[mcheemaa]

Summary

Adds support for the label argument on the @override directive, enabling progressive/percentage-based traffic splitting during subgraph migrations.

Motivation

Apollo Federation v2.7 introduced progressive @override which allows gradual migration of fields between subgraphs by controlling the percentage of traffic routed to each. This is useful for safely migrating high-traffic fields.

Apollo Documentation: https://www.apollographql.com/blog/safer-migrations-of-fields-using-progressive-rollouts

Usage

class MySchema < GraphQL::Schema
  federation version: '2.7'
end

# Routes 10% of traffic to this subgraph, 90% to 'products'
field :in_stock, Boolean, null: false, override: { from: 'products', label: 'percent(10)' }

Generated SDL:

type Product {
  inStock: Boolean! @federation__override(from: "products", label: "percent(10)")
}

Changes

• lib/apollo-federation/field.rb - Added optional label argument to @override directive
• lib/apollo-federation/schema.rb - Made federation version configurable in @link URL (>= 2.3 uses specified version, otherwise defaults to 2.3 for backwards compatibility)
• spec/apollo-federation/service_field_v2_spec.rb - Added tests for label argument and version configurability
• README.md - Updated documentation

Backwards Compatibility

• Existing override: { from: 'X' } usage continues to work unchanged
• Schemas using federation version: '2.0' still output v2.3 in the @link URL (current behavior)
• The label argument is optional

[swcollard]

Hello @mcheemaa

Unfortunately we are not actively maintaining this repo or accepting contributions at the time, but are considering getting back to it soon.

Given that apollo-federation-ruby is currently supporting Apollo Federtion v2.3, I'm also hesitant to accept a single feature from v2.7 without bringing support for the whole library up to spec with that version of Apollo Federation.