An uncommon but somewhat difficult to digagnose issue is dealing with
improperly-seeded databases. In such cases, instance-signed fetches will
fail with a ActiveRecord::RecordNotFound error, usually caught and handled
as generic 404, leading people to think the remote resource itself has not
been found, while it's the local instance actor that does not exist.

This commit changes the code so that failure to find the instance actor
automatically creates a new one, so that improperly-seeded databases do
not cause any issue.

* Search account domain in lowercase

* fix rubocop error

* fix spec/models/account_spec.rb

* Add support for an instance actor

* Skip username validation for local Application accounts

* Add migration script to create instance actor

* Make Codeclimate happy

* Switch to id -99 for instance actor

* Remove unused `icon` and `image` attributes from instance actor

* Use if/elsif/else instead of return + ternary operator

* Add instance actor to fresh installs

* Use instance actor as instance representative

Use instance actor for forwarding reports, relay operations, and spam
auto-reporting.

* Seed database in test environment

* Fix single-user mode

* Fix tests

* Fix specs to accomodate for an extra `Account`

* Auto-reject follows on instance actor

Following an instance actor might make sense, but we are not handling that
right now, so auto-reject.

* Fix webfinger lookup and serialization for instance actor

* Rename instance actor

* Make it clear in the HTML view that the instance actor should not be blocked

* Raise cache time for instance actor as there's no dynamic content

* Re-use /about/more with a flash message for instance actor profile

* Record account suspend/silence time and keep track of domain blocks

* Also unblock users who were suspended/silenced before dates were recorded

* Add tests

* Keep track of suspending date for users suspended through the CLI

* Show accurate number of accounts that would be affected by unsuspending an instance

* Change migration to set silenced_at and suspended_at

* Revert "Also unblock users who were suspended/silenced before dates were recorded"

This reverts commit a015c65d2d.

* Switch from using suspended and silenced to suspended_at and silenced_at

* Add post-deployment migration script to remove `suspended` and `silenced` columns

* Use Account#silence! and Account#suspend! instead of updating the underlying property

* Add silenced_at and suspended_at migration to post-migration

* Change account fabricator to translate suspended and silenced attributes

* Minor fixes

* Make unblocking domains always retroactive

* Fix admin validation being too strict about usernames

Fix #10446

* Strip Setting.site_contact_username consistently throughout the codebase

* Use Contact User as Relay, Report, Subscribe.

* Use Account.representative to fetch contact user.

* Use find_local.

* No reason to use Account.representative in subscribe_service.

* Don't required representative!

* Fallback is included in Account.representative method.

Comparison was downcasing only one side, therefore if previously
existing account had a non-lowercase spelling, it would be ignored
when checking for duplicates.

New rake task `mastodon:maintenance:find_duplicate_usernames` will
help find constraint violations that might have occured from the
presence of this bug.

Bump version to 2.3.3

* Move specs for account finder methods to concern spec

* Move account finder methods to concern

* Improve spec wording

* Use more explicit comparison to ensure correct return value

* Add coverage for .find_local! and .find_remote!

* Add some methods to the finder

* Use arel on matching_username method

* Avoid ternary in matching domain method

* Simplify finder methods

* Use an AccountFinder class to simplify lookup