* Speed up some rake tasks by moving execution to Sidekiq

mastodon:media:remove_silenced
mastodon:media:remove_remote
mastodon:media:redownload_avatars
mastodon:feeds:build

* Fix code style issue

* User agent for WebFinger

* local_domain → web_domain

* 'http' is away accidentally...

* Revert "Fixes/do not override timestamps (#7331)"

This reverts commit 581a5c9d29.

* Document Snowflake ID corner-case a bit more

Snowflake IDs are used for two purposes: making object identifiers harder to
guess and ensuring they are in chronological order. For this reason, they
are based on the `created_at` attribute of the object.

Unfortunately, inserting items with older snowflakes IDs will break the
assumption of consumers of the paging APIs that new items will always have
a greater identifier than the last seen one.

* Add `override_timestamps` virtual attribute to not correlate snowflake ID with created_at

* No need to re-require sidekiq plugins, they are required via Gemfile

* Add derailed_benchmarks tool, no need to require TTY gems in Gemfile

* Replace ruby-oembed with FetchOEmbedService

Reduce startup by 45382 allocated objects

* Remove preloaded JSON-LD in favour of caching HTTP responses

Reduce boot RAM by about 6 MiB

* Fix tests

* Fix test suite by stubbing out JSON-LD contexts

* Add support for separate Redis for cache

CACHE_REDIS_URL to allow using a different Redis server for cache
purposes, with cache-specific configuration such as key eviction

* Fix code style issues

Closes #7221

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

HTTP connections must be explicitly closed in many cases, and letting
perform method close connections makes its callers less redundant and
prevent them from forgetting to close connections.

Fix #6816, fix #6790

* add detailed SMTP settings setup in mastodon:setup

* add localhost SMTP settings setup in mastodon:setup

* SMTP settings setup should exit after successful delivery of test mail

Media attachments are part of the association cache of statuses,
since they are presumed to be immutable. Unless this cache is
cleared manually, the statuses will continue to look like they
have media embedded.

But do not upscale when they are smaller

The default locale is now set by config.