feat(functions): send function variable scope on deploy

[tkkhq]

Tracking

• Tracks: https://konghq.atlassian.net/browse/VOL-985
• Related: https://github.com/Kong/volcano-hosting/pull/990

Why

• function deployments currently send no function-specific variable selection, so the platform must inject every project variable
• large project environments can exceed Lambda's 4,096-byte limit even when a function uses only a few variables

Summary

• add variable_scope and variables to function entries in volcano-config.yaml
• send declared scoped variables through config deploy, cloud batch deploy, single-function deploy, and local deploy
• preserve the existing all-variable behavior when scope fields are omitted
• round-trip declared variable scope through config pull and strict manifest parsing
• regenerate the API client from the hosting contract
• document function variable declarations and dynamic-reference requirements
• rely on hosting for direct-reference detection and exact environment-size validation because the CLI deploy path does not have project variable values

Verification

• make check