Change account suspensions to be reversible by default

[Gargron]

Fix #6954

Instead of instantly deleting all account-owned data when suspending, hide it in the API layer. Instead of returning a HTTP 410 error for accounts that have been suspended, return an empty account with a new attribute suspended. Add a "suspended" account view to the web UI. Do not immediately send Delete activities to other servers.

This allows suspensions to be losslessly reversible, which helps with accidents, mistakes and appeals. It also allows providing the suspended user with a backup for GDPR compliance. Schedule real deletion after 30 days, while allowing admins to still override and speed up that process.

Federation-wise, this PR does not include any changes. This means that a locally suspended account continues to be visible on other servers like nothing happened for 30 days (but obviously cannot post or interact with anyone anymore). Federation support needs to be added in a future PR.

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Extracted into separate PRs:

• Refactor how public and tag timelines are queried #14728
• Fix various warnings in rspec #14729
• Remove obsolete IndexedDB operations from web UI #14730
• Refactor feed manager #14761
• Change REST API to return empty data for suspended accounts #14765
• Change web UI to show empty profile for suspended accounts #14766
• Refactor settings controllers #14767

[ClearlyClaire]

Mostly ok with this (except for the missing AP support and #14775 but those can be fixed in later PR) except for concerns about code being split from SuspendAccountService into DeleteAccountService (which is a good idea nevertheless):

• SuspendAccountService doesn't set suspended_at anymore, which seems counterintuitive and may not be fine with all callers
• I believe some parts of the code are calling SuspendAccountService when they should really be calling DeleteAccountService:
  • lib/mastodon/domains_cli.rb
  • lib/mastodon/accounts_cli.rb
  • app/lib/activitypub/activity/delete.rb
  • app/models/form/account_batch.rb

[ClearlyClaire]

I'm worried about SuspendService not setting suspended_at anymore… this basically requires the caller to mark the account as suspended. Maybe this is fine? I'm not sure.

[Gargron]

An issue I have run into before is I suspended someone and then I wanted to cancel it. I unsuspended quickly, but when the background job kicked in, it reset the account back to suspended. This is something I wanted to avoid.

[ClearlyClaire]

Wouldn't that still be an issue with the service removing stuff from TLs? And wouldn't that be fixed anyway by UnsuspendAccountService nullifying the suspended_at attribute?

[Gargron]

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