CI: Publish reports

[nomeata]

Our old CI was able to publish reports of various kinds (profiling reports, rendered documentation etc.) for each build. It even had a stable URL for “latest build report on branch X”, which we could link from the top-level README.

It would be good to recreate that using our Github Actions CI somehow. I am not sure what the best way is, though, so this needs some good ideas/research.

[nomeata]

@krpeacock recommends netlify, which we already use in the agent-* repos.

If someone in the org can configure the NETLIFY_AUTH_TOKEN and NETLIFY_SITE_ID secrets for the motoko repo, I can set up the deployment.

[nomeata]

I guess with #3113 I can close this. We could also use netlify if we want per-PR reports, but so far that is not a strong demand, it seems.