Move curl and httpie to final layer in dockerfile

[dylanmcreynolds]

Checklist

• Add a Changelog entry

#794 attempted to add curl and httpie to the docker image as a tool to be used in health checks. However, it was added to the builder layer, not the runner layer and hence not available at run time. This PR moves this installation.

Before this change:

docker exec -it ta991 bash
root@16a473d8c0e1:/deploy# curl
bash: curl: command not found
root@16a473d8c0e1:/deploy# 

After:

docker exec -it a901 bash
root@a90185b67888:/deploy# curl
curl: try 'curl --help' or 'curl --manual' for more information
root@a90185b67888:/deploy# 

[danielballan]

I should have tested that before merging. Heads up @Kezzsim.