chore: support testing user and system config levels in CI

[amoeba]

Adds a mechanism for running tests for the user and system config levels and adds a basic installation test for both config levels. The goal here is not to completely replicate the existing tests but to give us a way to test special cases of interest.

The approach here creates a new test suite class and standalone files instead of mixing them into other test suites and they are intentionally hard to run because they are potentially dangerous. And I wasn't able to find a good mechanism to do something more like Python or Rust where it's easier to mix tests together.

Tests are in integration_user_test.go and integration_system_test.go. I split these up because, in CI, I want to test the user level tests without sudo and the system level tests with sudo. There are other ways to work around this but I feel better just testing what the users would run directly.

You have to run the tests like,

# user
$ DBC_RUN_INTEGRATION_TESTS=1 go test -tags test_integration,test_system
#system
$ DBC_RUN_INTEGRATION_TESTS=1 go test -tags test_integration,test_user

This PR enables them in CI for all commits.

Closes #210

[amoeba]

Closing in favor of #239.