Include a short summary of enabled components as part of `bash-it doctor`

[NoahGorny]

Maybe we should include a short summary of enabled components as part of bash-it doctor. So instead of having to run several commands, we just run one command to produce the required output...

The list of components could be condensed to only show the enabled ones on one line (one for aliases, one for completions, one for plugins), instead of the line-by-line output that bash-it show currently produces.

Originally posted by @nwinkler in #1740 (comment)

[cornfeedhobo]

Yeah, I kinda like the idea of overloading doctor to push people to use it more and get ahead of any misconfigurations.