chore: use modern keycloak types

[alukach]

What I'm changing

This codebase currently uses @types/keycloak-js which was last updated 8 years ago and is now deprecated:

Instead, we now use the types packages with keycloak-js

How I did it

1. Rm @types/keycloak-js
2. Set moduleResolution in tsconfig.json from node to bundler. node is for versions of Node <v10. Seeing as we're using Rollup, bundler feels appropriate. This allows TS to find the Keycloak types.
3. Update types
4. For reasons that aren't entirely clear to me, I needed to also exclude some test files from packaging and install a testing library