When running `bundle exec rails assets:precompile` inside docker build, with `site_title` it requires a DB connection, where as `Setting.default_settings['site_title']` doesn't.
Running a docker build without this commit, the following error is reported:
```
...
[build-hometown:5785] ** Execute assets:generate_static_pages
[build-hometown:5786] rails aborted!
[build-hometown:5787] ActionView::Template::Error: could not connect to server: Connection refused
[build-hometown:5788] Is the server running on host "localhost" (127.0.0.1) and accepting
[build-hometown:5789] TCP/IP connections on port 5432?
[build-hometown:5790] could not connect to server: Cannot assign requested address
[build-hometown:5791] Is the server running on host "localhost" (::1) and accepting
[build-hometown:5792] TCP/IP connections on port 5432?
[build-hometown:5793] /opt/mastodon/vendor/bundle/ruby/2.6.0/gems/pg-1.1.4/lib/pg.rb:56:in `initialize'
[build-hometown:5794] /opt/mastodon/vendor/bundle/ruby/2.6.0/gems/pg-1.1.4/lib/pg.rb:56:in `new'
[build-hometown:5795] /opt/mastodon/vendor/bundle/ruby/2.6.0/gems/pg-1.1.4/lib/pg.rb:56:in `connect'
...
```
I can provide the full trace logs if needed.
- 500.html generated with admin-set default locale if set
- Error page `<title>` includes Mastodon site title
- 500 title changed to "This page is not
correct" (ref: <https://www.youtube.com/watch?v=2VCAP_seh1A>)
- 500 content appended with "on our end" to make clear it's
not user's fault
