[headless] Set up access manager before starting server

This became necesary to due an upstream change we missed when bumping
the dependency:

https://github.com/tipsy/javalin/commit/ab19ff91b7963313479779636c557770d93a5098
1 job for javalin-access-manager in 10 minutes and 7 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Test
passed #2612
test

00:10:07