Reduce startup time of keycloak

[rocketeerbkw]

When keycloak starts from a blank slate, we run a start.sh script that preconfigures everything needed for lagoon. When booting with an existing database, there's still a decent wait time while it checks the config until it signals it's "ready."

This startup time can be quite long which creates annoyances in local development and wasted time in CI.

Tasks:

• Measure current startup times for a baseline
  • Check locally and in CI
• What is an acceptable wait?
  • Can we fail/warn tests if we exceed
• Test/compare different solutions
  • Upgrade keycloak
  • Use native keycloak export/import
  • Parallelize startup script
  • Use a pre-loaded keycloak-db image

[rocketeerbkw]

Here's some results from my testing (i'll update as I test more)

Init with empty database:
keycloak 7
7:15.6
6:48.8
6:42.3
6:40.8
6:41.8

keycloak 16
4:41.8
4:26.4
4:20.2
4:19.4
4:23.5

[tobybellwood]

initial poc in #3499