Roles: Consolidate infrastructure roles

[pllim]

I finally got around to "Step 1" from the roles breakout session from Astropy Coordination Meeting 2023.

Who attended: me, @eteq, @hamogu, @weaverba137, @aaryapatil, @saimn

Exact notes that is relevant here:

• Expand infrastructure
  • Change Specialist to Project Infrastructure Tech Lead and reduce scope to "set up and maintain CI” and “moving between repo" because others are covered by “core” roles already.
  • Have sub-roles according to broad categories w.r.t. flow chart from State of Infrastructure this morning.

My interpretation of those notes is this PR.

Out of scope: Adding/removing people.

Preview: https://output.circle-artifacts.com/output/job/c59e5d73-47f0-4fb7-a8d5-03f8163ad418/artifacts/0/html/team.html