build: Specify default-members in Cargo toml

This way we don't build xtask by default, hence we don't build
unnecessary dependencies when performing release builds on CI.

Cargo.toml

@@ -61,6 +61,20 @@ members = [
     "xtask",
     "test-suite",
 ]
+default-members = [
+    "crates/modules/file-system-monitor",
+    "crates/modules/process-monitor",
+    "crates/modules/network-monitor",
+    "crates/modules/rules-engine",
+    "crates/modules/logger",
+    "crates/modules/desktop-notifier",
+    "crates/pulsar-core",
+    "crates/bpf-common",
+    "crates/bpf-builder",
+    "crates/engine-api",
+    "crates/validatron",
+    "crates/bpf-filtering"
+]
 
 [workspace.package]
 version = "0.6.0"