feat: add plan cmd and plan generator

[devsergiy]

Motivation and Context

We need a way to batch-produce query plans for a list of queries from the source folder with the given router's execution configuration.
This PR adds a new cmd to generate query plans which outputs pretty printed plans

It could be used like this

go run cmd/plan-generator -execution-config=config.json -operations=./operations -plans=./plans

Checklist

• I have discussed my proposed changes in an issue and have received approval to proceed.
• I have followed the coding standards of the project.
• Tests or benchmarks have been added or updated.
• Documentation has been updated on https://github.com/wundergraph/cosmo-docs.
• I have read the Contributors Guide.

[github-actions]

Router image scan passed

✅ No security vulnerabilities found in image:

ghcr.io/wundergraph/cosmo/router:sha-b1553a8e0569b02afe08419a2a619265608f8494