Build: new notification system for build notifications

[agjohnson]

This came from a discussion at our offsite. I put up an internal discussion at https://github.com/readthedocs/meta/discussions/126 in case there is anything left to discuss. But if not, starting with the build notification changes is probably where we'd start with this work I imagine.

To distill this conversation heavily:

We want to overhaul the way we output notifications and messages from the build. This would replace:

• Error strings output from exceptions during build
• Error strings output from commands during build
• Template logic showing blocks in templates for error/info messages

Instead:

• During a build, multiple messages could be output from the build.
• Each message would have more attributes than django notification messages.
• Each message would have richer content than our error messages now, probably HTML so we can actually write proper links.
• We'd track state around the notification, and dismiss notifications when underlying conditionals resolve

#3399 was the original start of this, but I hesitate to reuse that issue as it was used for multiple changes already. Perhaps it's best to close that up and move the relevant discussion.

[agjohnson]

Also noted from today, latex pdf builds could emit a warning when we get a non-zero exit code.

[humitos]

Related issues/docs

• Better UX to comunicate warnings on the build page #4226 ✅
• Improve build error/warning suggestions #3399 ✅
• https://github.com/readthedocs/meta/discussions/126 ✅
• Tip message for config file when already using it #5909 ✅
• Build: plan for better description of build state and build status #9110 ✅
• Consolidate build detail view notification patterns #9279 ✅
• Move pseudo-notification for webhooks from project pages #4235 ✅

[humitos]

I reviewed all the issues linked and wrote down some thoughts that I pasted at https://gist.github.com/humitos/e9782439bee9ad6c5897a5557c163244

This is not the final version, but just some ideas / concepts and notes that I took while reading all those issues. We have a lot of duplicated information around and I wanted to summarize them all in just one document.