Badges: add code quality badge to project homepage

[davidwatkins73]

Description

The LGTM (looks good to me) service we were using to measure code quality was deprecated some time ago.
This issue should find a replacement which gives us the same immediate feedback when opening the project. Clearly actionable issues should be easy to discover.

Resourcing

We would like to collaborate on this task

[davidwatkins73]

We currently have no preference on which tool to use. Happy for suggestions !