Build: add more output details to the build detail page

A secondary discussion that came from https://github.com/readthedocs/readthedocs.org/issues/7005 was around some of the additions lined up for the build detail page, which are roughly tangential to adding a debug flag attribute to the BuildCommand model. These additions would aim to increase the user's understanding of the commands and command steps. There are other additions for the build detail page, but just to focus on improvements to the command listing and/or debug output view:

• Show the step that the command executed under
• Show more debug level commands
• Show command descriptions for some commands

The next step is to experiment more with the display here. All of these changes could negatively affect the build command list, so I'll want to go through a few ideas before settling on what works best here.

A few problems we're solving here:

• We aren't surfacing where in the build process the command is executed, which would make build.jobs easier to follow and understand
• We execute commands that aren't clear, for example the cat commands might not make sense if the user isn't familiar with POSIX shells. An annotation or description would help explain what is happening to the user.