[feature] Public list of suspended domains

[f0x52]

Description

Adds a opt-in config 'InstanceExposeSuspendedWeb' for serving a list of suspended domains on /about/suspended.
fixes #378

Ideally this will later be configurable in the settings interface, but that depends on #1360

Checklist

• I/we have read the GoToSocial contribution guidelines.
• I/we have discussed the proposed changes already, either in an issue on the repository, or in the Matrix chat.
• I/we have performed a self-review of added code.
• I/we have written code that is legible and maintainable by others.
• I/we have commented the added code, particularly in hard-to-understand areas.
• I/we have made any necessary changes to documentation.
• I/we have added tests that cover new code.
• I/we have run tests and they pass locally with the changes.
• I/we have run go fmt ./... and golangci-lint run.

NLnet Milestone 10.a: Page for displaying block lists (if instance allows showing it)

[tsmethurst]

The new page and its styling look really nice. Just a couple comments, lemme know what you think :)

[turtlegarden]

this looks amazing! Until now I used a hacky solution and this looks much better

[f0x52]

Rebased, good to go now!

[tsmethurst]

almost there!