Add a plugin dependency section to Site Health

[desrosj]

Site Health is a great way to provide an indication something may be broken (missing dependencies), provide additional information about how to go about resolving the problem, and link out to more documentation when necessary.

For support teams, this information could be really helpful when trying to resolve a problem on a site.

At a minimum, the section could list any missing dependencies and maybe which plugins require them. At a maximum, there could be a dependency tree of sorts that helps visualize the shared requirements for their plugins.