* chore: add k6 and define dev container

* stamp: move image assets into `/assets`

* stamp: adjust default listening port of `run.sh`

* stamp: suppress unnecessary logging

* stamp: change load-testing endpoint

* stamp: update `README.md`

* stamp: move benchmark script into `scripts`

* stamp: update `README.md` (2)

* stamp: add `hyperfine` package into dev container image

* stamp: separate development-related section into `DEVELOPERS.md`

* stamp: update `README.md` (3)