Fixes #16435

Fix #2744

Move public domain blocks information to about page

* 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

Bumps [webpacker](https://github.com/rails/webpacker) from 3.5.5 to 4.0.2.
- [Release notes](https://github.com/rails/webpacker/releases)
- [Changelog](https://github.com/rails/webpacker/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rails/webpacker/compare/v3.5.5...v4.0.2)

Signed-off-by: dependabot[bot] <support@dependabot.com>
Co-authored-by: Yamagishi Kazutoshi <ykzts@desire.sh>

* add several missing alt tags

* remove alt text from mascot images

Follow-up to #8142

* Redesign landing page (again)

* Move login form in small version to the right column

* Display closed registrations message

* Add site setting for the hero image

* Fix test

* Increase spacing, maximum width, change call to action section

They were redundant, and also had a inconsistency; the button for
"other instances" had an icon for the external link in "more" page, but
it didn't in the other pages.

This unifies the implementation, and the external link icon is now shown
in all the about pages.

* Improve OpenGraph tags for about pages

* Add thumbnail admin setting

* Fix error

* Fix up

* Add Mastodon::Source.url

* Update spec

* Refactor

Move things frmo Mastodon::Source to Mastodon::Version

apply same style class to the About description on both the landing page
and the about/more page

* Redesign extended information page

* Remove unused keys

* Add $ui-base-lighter-color variable to SCSS

* add haml_lint to Gemfile

* add .haml-lint.yml

* fix warnings of haml_lint

* Adds version.

* Cleans up code.

* Removes standalone endpoint and adds version to instance endpoint.

* Addresses feedback from #2181.

* Simplify render in mailer views

* Simplify render in about/more view

* Simplify render in accounts follow views

* Simplify render in recovery code views

* Simplify render in stream entry embed

* Simplify render in stream entries status partial

* Simplify render in authorize follow new view

* Move site title helper to instance helper (name change only)

* Remove newline in <title> tag

* Add site_hostname helper method to wrap up local_domain value

* Use site_hostname helper in places that need local_domain value

* Correct site_contact_email typo

* Separate about more page into partials, add specs

* Add InstancePresenter to expose site details

* Clean up about controller, use instance presenter