feat(myapi): add minimal service with GET /health and POST /echo

[AdrianxSanchez]

This PR adds a minimal HTTP service myapi:

• GET /health -> {"status":"ok"}
• POST /echo -> echos JSON body

How to run locally:
go run ./cmd/myapi

Quick test:
curl -s localhost:8080/health
curl -s -X POST localhost:8080/echo
-H 'Content-Type: application/json'
-d '{"hola":"ux"}'

Branch name follows the policy: feature/myapi-service
Commit message follows Conventional Commits.