Sidekiq was failing to boot in dev due to the following error. It seems
like constantizing stuff before the autoloader has kicked in caused
stuff to go weird. Root cause has not been identified but there is no
reason for us to have to warm up the cache during the initialization of
Rails.
```
2021-09-06T04:28:43.338Z pid=112028 tid=26vc WARN: NameError: uninitialized constant #<Class:0x0000564b365040d8>::RateLimiter
2021-09-06T04:28:43.338Z pid=112028 tid=26vc WARN: /discourse/app/models/post.rb:9:in `<class:Post>'
/discourse/app/models/post.rb:6:in `<top (required)>'
/ruby/2.7.4/lib/ruby/gems/2.7.0/gems/zeitwerk-2.4.2/lib/zeitwerk/kernel.rb:26:in `require'
/ruby/2.7.4/lib/ruby/gems/2.7.0/gems/zeitwerk-2.4.2/lib/zeitwerk/kernel.rb:26:in `require'
```
Previously we had many places in the app that called `hostname` to get
hostname of a server. This commit replaces the pattern in 2 ways
1. We cache the result in `Discourse.os_hostname` so it is only ever called once
2. We prefer to use Socket.gethostname which avoids making a shell command
This improves performance as we are not spawning hostname processes throughout
the app lifetime
Under extreme load on large databases certain regular jobs can take quite
a while to run. We need to ensure we never starve a sidekiq from running
mini scheduler, cause without it we are unable to queue stuff such as
heartbeat jobs.
This reduces chances of errors where consumers of strings mutate inputs
and reduces memory usage of the app.
Test suite passes now, but there may be some stuff left, so we will run
a few sites on a branch prior to merging
This commit also cleans up a bunch of pointless noise each time we boot app
- narrative was loading i18n cause redefinition of consts
- discourse.rb was loaded twice as was auth
- bin/unicorn now does all the smart things and boots unicron in dev
- bin/rails s will boot unicorn with no params
- remove bin/puma which only causes confusion
