migrate sysadmin roadmap in trac wiki

right now we have the sysadmin roadmap in three places:

• https://pad.riseup.net/p/CYOUx21kpxLL_5Eui61J-tpa-roadmap-2020
• https://pad.riseup.net/redirect#https%3A//help.torproject.org/tsa/roadmap/2020/
• https://trac.torproject.org/projects/tor/wiki/org/teams/SysadminTeam

let's move all of this in one, or at most two, location, probably the latter since we're now using tickets for february and march.

we can keep the free-form text thing for the remaining months for now.