Merge commit '34cd7d6585992c03298c175ab5d22ad059b58cdb' into glitch-soc/merge-upstream

Conflicts:
- `CONTRIBUTING.md`:
  Upstream changed the file, while we had a different one.
  Updated the common parts.
- `README.md`:
  Upstream changed the file, while we had a different one.
  Updated the common parts.
- `app/helpers/application_helper.rb`:
  Upstream added helpers where glitch-soc had extra ones.
  Added upstream's new helpers.
- `app/models/form/admin_settings.rb`:
  Upstream added some custom handling of one setting, while
  glitch-soc had additional code.
  Ported upstream's code.
- `lib/mastodon/version.rb`:
  Upstream moved some things to `config/mastodon.yml`.
  Did the same.
- `spec/requests/api/v1/accounts/credentials_spec.rb`:
  I don't know honestly.

CONTRIBUTING.md

@@ -51,7 +51,7 @@ You can contribute in the following ways:
 If your contributions are accepted into Mastodon, you can request to be paid through [our OpenCollective](https://opencollective.com/mastodon).
 
 Please review the org-level [contribution guidelines] for high-level acceptance
-criteria guidance.
+criteria guidance and the [DEVELOPMENT] guide for environment-specific details.
 
 [contribution guidelines]: https://github.com/mastodon/.github/blob/main/CONTRIBUTING.md
 
@@ -94,3 +94,5 @@ It is not always possible to phrase every change in such a manner, but it is des
 The [Mastodon documentation](https://docs.joinmastodon.org) is a statically generated site. You can [submit merge requests to mastodon/documentation](https://github.com/mastodon/documentation).
 
 </blockquote>
+
+[DEVELOPMENT]: docs/DEVELOPMENT.md