Try building docker images

[DMRobertson]

• Use the workflow in Reusable workflow to build and optionally publish docker images backend-meta#2 to build and publish docker images for the main branch
• Use poetry to manage the venv within the container

This worked in this CI run to publish this.

[DMRobertson]

See matrix-org/backend-meta#2 for the workflow

[squahtx]

lgtm!

For some reason synapse calls the secrets DOCKERHUB_USERNAME and DOCKERHUB_TOKEN, without the underscore. I believe Synapse is the odd one out, since the secrets defined at the organization level include the extra underscore.

[DMRobertson]

For some reason synapse calls the secrets DOCKERHUB_USERNAME and DOCKERHUB_TOKEN, without the underscore. I believe Synapse is the odd one out, since the secrets defined at the organization level include the extra underscore.

I'll change the workflow to include the extra underscore, to avoid this potential footgun. And I can later change Synapse to use the org-level secret.

[DMRobertson]

This failed when I tested it with my account, but I think that's because the access token expired. I'm going to revert to 8f7b773, commit this, and then take it from there. We can refine/fixup later.