Multi-Provider support

[AleksandrasMaliuginas-vinted]

Why

As defined in Open feature specification SDKs have to support multiple providers with evaluation strategies.

What

Add support for Multi-Provider setup in ruby sdk. Also add support for First Match, Comparison, and Custom Strategies.

Other languages that support Multi-Provider:

• GO: https://pkg.go.dev/go.openfeature.dev/openfeature/v2/providers/multi#section-readme
• JS: https://openfeature.dev/blog/openfeature-multi-provider-release/