epic: Support gRPC service config

[mbobakov]

Background

My project serves as a client resolver for Consul, fetching endpoints and providing them to gRPC clients. To enhance the flexibility of configurations, I propose adding support for gRPC service config storage in the Consul KV store.

Feature Request

I want to store gRPC service configurations as keys in the Consul KV store. This will enable users to define service-specific gRPC settings centrally in Consul, improving manageability and reconfigurability.

Proposed Implementation

ConsulKV Store Integration:

Integrate the ConsulKV store functionality to read gRPC service configurations.
Allow users to define gRPC service config as JSON in Consul.

Path to the service config could be provided as URL parameter: Link

In case of failed config parsing, we could throw the log error and continue to work or throw the error and exit. WDYT?

Additional Information

Link to gRPC service config documentation
Example in DNS resolver. They lookup for TXT record

Acceptance Criteria:

• The resolver successfully fetches and applies gRPC service config from the Consul KV store.
• The test covers the usecase of gRPC service config fetch
• Documentation is updated to reflect the new feature.