Explore performance testing for REST/JSON:API endpoints

Problem/Motivation

Mentioned in 📌 Optimize UserLoginController by remove duplicate entity queries RTBC about exploring the idea of adding performance testing for REST/JSON:API endpoints. Reason I opened this was there may be a number of sites using headless or if headless layout builder is merged, would be good to test some endpoints (or some)

Steps to reproduce

NA

Proposed resolution

TBD

Remaining tasks

Decide if worth it
If yes implement

User interface changes

NA

API changes

NA

Data model changes

NA

Release notes snippet

NA