feat(agent)!: add support for mTLS authentication in gRPC server (#54)

* refactor(fancontroller): improve fan controller validation logic and error handling for temperature steps

* refactor(agent): restructure gRPC server implementation by moving it to a new api package for better organization and maintainability

* feat(agent): implement gRPC server for managing compute blade agents and add graceful shutdown support
refactor(agent): restructure agent code by moving API logic to a dedicated file and improving error handling
fix(agent): update logging messages for clarity and consistency across the agent's operations
chore(agent): remove unused API code and consolidate event handling logic for better maintainability
style(agent): improve code formatting and organization for better readability and adherence to conventions

* feat(agent): add support for TLS configuration in gRPC server

* feat(api): add gRPC server authentication

* fix

* feat(config): add listen mode configuration to support tcp or unix sockets
feat(agent): implement listen mode in gRPC service to allow flexible socket types
feat(bladectl): enhance configuration loading and add support for TLS credentials
fix(bladectl): improve error handling for gRPC connection and event emission
style(logging): change log level from Warn to Info for better clarity in logs

* add logging middleware + fixes

* fix remote-connection to gRPC API Server

debugging the SAN issues took the soul out of me... And then the stupid
mistake in cmd_root where I didn't construct the TLS credentials
correctly... Oh dear...

* cleanup

* cleanup

* cleanup commands

* cleanup

* make README.md nicer

* Update cmd/agent/main.go

Co-authored-by: Matthias Riegler <github@m4tbit.de>

* Update cmd/bladectl/cmd_root.go

Co-authored-by: Matthias Riegler <github@m4tbit.de>

* move bladectl config into correct directory

* fix bugs

* // FIXME: No dead code

* nit: code style

* nit(YAGNI): you aint gonna need it. Don't make life harder than it needs to be

* nit(YAGNI): you aint gonna need it. Don't make life harder than it needs to be

* nit(YAGNI): you aint gonna need it. Don't make life harder than it needs to be

* nit(cmd_identify)

---------

Co-authored-by: Matthias Riegler <github@m4tbit.de>

pkg/util/file_exists.go

@@ -0,0 +1,9 @@
+package util
+
+import "os"
+
+// FileExists checks if a file exists at the given path and returns true if it does, false otherwise.
+func FileExists(path string) bool {
+	_, err := os.Stat(path)
+	return err == nil
+}

pkg/util/host_ips.go

@@ -0,0 +1,43 @@
+package util
+
+import "net"
+
+func GetHostIPs() ([]net.IP, error) {
+	var ips []net.IP
+
+	ifaces, err := net.Interfaces()
+	if err != nil {
+		return nil, err
+	}
+
+	for _, iface := range ifaces {
+		// Skip down or loopback interfaces
+		if iface.Flags&net.FlagUp == 0 || iface.Flags&net.FlagLoopback != 0 {
+			continue
+		}
+
+		addrs, err := iface.Addrs()
+		if err != nil {
+			continue // skip interfaces we can't read
+		}
+
+		for _, addr := range addrs {
+			var ip net.IP
+			switch v := addr.(type) {
+			case *net.IPNet:
+				ip = v.IP
+			case *net.IPAddr:
+				ip = v.IP
+			}
+
+			// Skip loopback or unspecified
+			if ip == nil || ip.IsLoopback() || ip.IsUnspecified() {
+				continue
+			}
+
+			ips = append(ips, ip)
+		}
+	}
+
+	return ips, nil
+}