ara should probably record the version of the callback plugin and API server

What is the idea ?

The version of the http client is sent as a user-agent (here) and it shows up in server logs kind of like this:
"GET /api/v1/playbooks?order=-started&limit=50 HTTP/1.1" 200 66635 "-" "ara-http-client_1.5.9.dev51"

The version isn't saved in the database like the Ansible version is, though.
It may be useful to save it as there may be disparities with different behaviors across versions.

I think ideally everyone has the same version everywhere but mismatches are bound to happen.

It would be inexpensive to implement even if just for troubleshooting and debugging purposes, just extra fields next to Ansible version:

ara/ara/api/models.py

Line 86 in ed20abc

ansible_version = models.CharField(max_length=255)

This is merged and will release in 1.6.0.