Require bridgetown when booting from Rack

[ayushn21]

In order to start Bridgetown by running the web server directly (bundle exec puma), we need to require "bridgetown" in the boot file.

Without it, we get all sorts of uninitialized constant errors.

This is one of those fixes where I'm not sure what I'm doing, and whether it'll have any bad consequences. I just hammered it until it worked and seems to be working fine in my tests.

@jaredcwhite is this a valid fix? Please don't merge it until we know for sure it's not gonna make things catch fire haha.

Part of #946

[jaredcwhite]

@ayushn21 Off the top of my head, I believe if we're completely bypassing Bridgetown's own CLI, we'd need to replicate calling Bridgetown.begin! which loads up the right Bundler context. Not sure where that could go exactly, and we'd want to make sure we don't accidentally call it twice.

[ayushn21]

@jaredcwhite ah ok cool, I'll have a poke around.

[ayushn21]

What if we say that running the web server directly won't trigger a site build ... it'll only run Bridgetown in a live context ... i.e. Roda routes + anything already in the output folder ... do we still need to call Bridgetown.begin! then?

[jaredcwhite]

@ayushn21 Yeah, the server/Roda context would still need the same bootup sequence. Running a build process is just what could happen after initial boot. See Bridgetown::PluginManager.setup_bundler for an example.

I think we may need some kind of additional global state to indicate if the boot sequence has already run…if not, the rack boot needs to kick it off immediately after require "bridgetown". I think…