[QoS] Use NoOp QoS for Unconfigured Services

[commoddity]

Objective

1. Use NoOp QoS to select a random endpoint for services that do not yet have a QoS implementation instead of outright rejecting the request.

2. Remove the requirement for defining services in the PATH config YAML.

Related issue: #104

Origin Document

The current behavior of PATH forces operators to define services in the YAML configuration, creating redundancy with Envoy Proxy.

By using Envoy as the single source of truth for "allowed services", PATH now only handles QoS services mappings without the need for operator configuration, improving clarity and reducing configuration complexity.

Links:

• Closing PR: [WIP] Integrate noop service into PATH #112
• Implementation PR (merge before [WIP] Integrate noop service into PATH #112): https://github.com/buildwithgrove/path/pull/1123
• Preceding PR: [QoS] Introduce v0 of Noop QoS module #106
• Envoy-Level Implementation: [ENVOY] feat: Envoy to set Service ID header from subdomain #102
• Related Discussion: https://discord.com/channels/824324475256438814/1263851886486880356/1318695800754405466

Goals

• Eliminate the redundant services field in PATH config YAML.
• Use Envoy Proxy as the single source of truth for which services a PATH instance allows requests for.
• Ensure unsupported services default to a NoOp QoS implementation.
• Update cmd/qos.go to build the gatewayQoSService map from QoS mappings.

Deliverables

• Remove the services field from the PATH YAML configuration schema.
• Update cmd/qos.go to initialize gatewayQoSService using config/service_qos.go.
• Modify Parser to use a NoOp QoS implementation for unsupported services.
• Rename config/service_alias.go to config/service_qos.go.
• Refactor and update documentation to reflect the authoritative service ID concept.
• Ensure make test_all passes after all changes.

Non-goals / Non-deliverables

• No changes to Envoy Proxy itself; this focuses solely on adapting PATH to the new validation model. (These changes are instead handled in [QoS] Use NoOp QoS for Unconfigured Services #114)

General Deliverables

• Comments: Add/update comments for new and modified logic.
• Testing: Add tests to verify the NoOp QoS default behavior and service mapping logic.
• Documentation: Update relevant documentation with the new workflow and terminology.

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Creator: @commoddity
Co-Owners: @Olshansk @adshmh