RFC healthcheck

[ericphanson]

This adds a healthcheck function which is basically an alternate show method:

julia> healthcheck(analyze_from_registry(find_package("DataFrames")))
DataFrames.jl
☑ Has code (16163 lines)
☑ Has docs (3431 lines)
☑ Has tests (16296 lines)
☑ Has license(s)
    MIT (✔ OSI-approved)
☑ Has CI (GitHub Actions)

julia> healthcheck(analyze_from_registry(find_package("CommonMark")))
CommonMark.jl
☑ Has code (3943 lines)
◻ Has docs
☑ Has tests (1215 lines)
☑ Has license(s)
    MIT (✔ OSI-approved)
    BSD-2-Clause (✔ OSI-approved)
    MIT (✔ OSI-approved)
    MIT (✔ OSI-approved)
    CC-BY-SA-4.0 (⨉ not OSI-approved)
☑ Has CI (GitHub Actions)

The idea is it could be used by a package author / maintainer themselves to quickly get a look at the status of their package and/or check off some boxes 🙂. It could also be autocommented in General PRs for package authors to get a sense of the "health" of the package/version they are releasing, and give a nudge towards good practices (and provide more info for passers-by).

Here I used empty boxes instead of Xs to try to be more encouraging.

Opening as draft for feedback; I feel like it could probably use some more tweaking still.

[giordano]

If the idea is to have something similar also for RegistryCI, perhaps we want to have multiple methods for different MIMEs (plain text vs markdown)? Or this can be show(::IO, ::MIME"markdown", ::Package)?