Add server init logic for SAML and DNS

[humphd]

Fixes #275.

We have a number of modules that require some kind of asynchronous setup step before the app can start. Currently, this includes:

• SAML: we need to download the IdP's metadata XML and use it to create an IdentityProvider instance
• DNS: in development, we need to create a hosted zone on the mock Rout53 server

In order to facility this kind of logic, I'm adding a step before the server is started that does any init() that a module might need done. All you have to do is export an async function, and we'll call it at startup.

The way that Remix hot-reloads work, I had to do a bit of gymnastics to preserve module state after a server-side reload. The current db.server.ts file shows a pattern to use: define a global variable and stick the instance data there, then restore it when the module is reloaded.

I've also moved the SAML code into app/lib/ like the other server modules.

To test this, do npm run build and npm run dev and you'll see something like this:

info: 🔌 setting up prisma client to localhost:3306
info: app initializing...
debug: SAML init: downloading IdP metadata from http://localhost:8081/simplesaml/saml2/idp/metadata.php
debug: DNS init: created hosted zone EPE35EFYJZJFNT8 for starchart.invalid
Watching Remix app in development mode...
💿 Built in 311ms
info: ✅ app ready: http://localhost:8080

Now the metadata is downloaded (SAML login should work) and a DNS hosted zone has been created (the DNS stuff in #274 should work in development).