Implement TLS API Support

* Added flags to point to TLS PEM files to use for exposing and connecting
  to an encrypted remote API socket with server and client authentication.
* Added TLS fields for system connection ls templates.
* Added special "tls" format for system connection ls to list TLS fields
  in human-readable table format.
* Updated remote integration and system tests to allow specifying a
  "transport" to run the full suite against a unix, tcp, tls, or mtls
  system service.
* Added system tests to verify basic operation of unix, tcp, tls, and mtls
  services, clients, and connections.

Signed-off-by: Andrew Melnick <meln5674.5674@gmail.com>

pkg/util/tlsutil/tls.go

@@ -0,0 +1,32 @@
+package tlsutil
+
+import (
+	"crypto/x509"
+	"encoding/pem"
+	"fmt"
+	"os"
+)
+
+func ReadCertBundle(path string) (*x509.CertPool, error) {
+	pool := x509.NewCertPool()
+	caPEM, err := os.ReadFile(path)
+	if err != nil {
+		return nil, fmt.Errorf("reading cert bundle %s: %w", path, err)
+	}
+	for ix := 0; len(caPEM) != 0; ix++ {
+		var caDER *pem.Block
+		caDER, caPEM = pem.Decode(caPEM)
+		if caDER == nil {
+			return nil, fmt.Errorf("reading cert bundle %s: non-PEM data found", path)
+		}
+		if caDER.Type != "CERTIFICATE" {
+			return nil, fmt.Errorf("reading cert bundle %s: non-certificate type `%s` PEM data found", path, caDER.Type)
+		}
+		caCert, err := x509.ParseCertificate(caDER.Bytes)
+		if err != nil {
+			return nil, fmt.Errorf("reading cert bundle %s: parsing item %d: %w", path, ix, err)
+		}
+		pool.AddCert(caCert)
+	}
+	return pool, nil
+}