Use Guard & Exit, Guard only, Exit only, and Middle only on all bandwidth by flag graphs

Should we use Guard & Exit, Guard only, Exit only, and Middle only on:

• https://metrics.torproject.org/bandwidth-flags.html and
• https://metrics.torproject.org/bwhist-flags.html
• the new graph from legacy/trac#28328 (moved)

I think it would be helpful to be consistent, but it's also not a big deal.

If we make the bandwidth-flags and bwhist-flags graphs use the same flags, should we merge the two graphs?

• https://metrics.torproject.org/bandwidth-flags.html and
• https://metrics.torproject.org/bwhist-flags.html