Roles: Add sub-roles for infrastructure and other related updates, remove Madison due to inactivity

[pllim]

Another stab at the infrastructure stuff in #519 .

• There is now a proper Infrastructure Team with sub-roles.
  • The existing ones are pretty comprehensive to begin with, so I mainly just move titles around.
  • Folded the website title into infrastructure, because I think it is.
• For some roles, I clarified and expanded their responsibilities. Most are based on what I already do, but I wish people with those roles would do instead.
• Added a new unfilled role for "metrics". This is because I think benchmarks and dashboard are important but they are broken, and we need a dedicated role for them going forward, if we ever want working benchmarks and dashboard again.
• Merged "Core astropy package maintainer (general)" and "Core astropy package maintainer (sub-package)", both now under "Core astropy package maintainer", but they retained their sub-roles. I needed to do this here because I needed to clarify some overlap between the "general" core maintainer with the "DevOps Specialist".

Incorporated later:

• Roles: Remove Madison due to inactivity #536

Preview: https://output.circle-artifacts.com/output/job/1197d6ec-ae8c-4a71-a3d2-8da7a525b1dc/artifacts/0/html/team.html

Out of scope: Removing/added names besides the one. We have agreed at the Astropy Coordination Meeting 2023 that names will be touched at a later stage.

Out of scope: Reordering the roles. That will also happen later as part of #412.

[pllim]

@hamogu , thanks for the comments. I believe I have addressed them. I also resolved the merge conflict and the preview magically works again!

[pllim]

Things have changed a little and there is conflict, so I am closing this without merge and will revisit with a new (and hopefully less controversial) PR.