Add test for systemwide config file support

There is now a new stage in the CICD workflow present, which will build
`bat` with the `BAT_SYSTEM_CONFIG_PREFIX` set to load the config file
from `/tests/examples/system_config/bat/config`, plus a basic set of
tests, to ensure the feature is working as expected. By default the
tests are set to ignored, as they need special setup before they can be
run.

tests/system_wide_config.rs

@@ -0,0 +1,29 @@
+use predicates::{prelude::predicate, str::PredicateStrExt};
+
+mod utils;
+use utils::command::bat_with_config;
+
+// This test is ignored, as it needs a special system wide config put into place.
+// In order to run this tests, use `cargo test --test system_wide_config -- --ignored`
+#[test]
+#[ignore]
+fn use_systemwide_config() {
+    bat_with_config()
+        .arg("test.txt")
+        .assert()
+        .success()
+        .stdout(predicate::eq("dummy-pager-from-system-config\n").normalize());
+}
+
+// This test is ignored, as it needs a special system wide config put into place
+// In order to run this tests, use `cargo test --test system_wide_config -- --ignored`
+#[test]
+#[ignore]
+fn config_overrides_system_config() {
+    bat_with_config()
+        .env("BAT_CONFIG_PATH", "bat.conf")
+        .arg("test.txt")
+        .assert()
+        .success()
+        .stdout(predicate::eq("dummy-pager-from-config\n").normalize());
+}