create integrator charm

[techalchemy]

• add s3 integrator charm
• add documentation
• add github workflows
• add test coverage
• add integrator library

Signed-off-by: Dan Ryan dan.ryan@canonical.com

[jnsgruk]

Mid way through another conversation, it's just struck me that this will also work as a Kubernetes sidecar charm with very minimal effort... :D

[deusebio]

Closing as this has been superseded by #2