Adds devbox for easy environment management.
In combination with `direnv`, the env is started automatically.
Without `direnv`, just do `devbox shell`.
Running Make as a task runner is phony.
A Taskfile is better suited for this.

Copying the binary into the Docker container doesn't work
if the host CPU architecture is different (like an M1 mac).
Since it's quick to build, we can just build the CLI
inside Docker.

This commit also re-enables support for the `--wait` flag,
which was commented out.

This commit gets rid of some custom validation code.
We don't have to validate the multiple-batch request body
in the CLI, since that is done in the v4 API client now.
This commit also adds support for the 'delete index' and 'clear objects'
actions.