feat(SSH): Add support for SSH endpoint (#473)

* feat(SSH): Add support for SSH endpoint

This commit adds support for SSH endpoint monitoring. Users can now configure an endpoint to be monitored using an SSH command by prefixing the endpoint's URL with ssh:\\. The configuration options for an SSH endpoint include the username, password, and command to be executed on the remote server. In addition, two placeholders are supported for SSH endpoints: [CONNECTED] and [STATUS].

This commit also updates the README to include instructions on how to configure SSH endpoints and the placeholders that can be used in their conditions. The README has been updated to include the new SSH-related options in the endpoints[] configuration object.

Here's a summary of the changes made in this commit:

    Added support for SSH endpoint monitoring
    Updated the documentation to include instructions on how to configure SSH endpoints and the placeholders that can be used in their conditions

core/endpoint_test.go

@@ -256,6 +256,7 @@ func TestEndpoint_Type(t *testing.T) {
 	type args struct {
 		URL string
 		DNS *DNS
+		SSH *SSH
 	}
 	tests := []struct {
 		args args
@@ -325,6 +326,16 @@ func TestEndpoint_Type(t *testing.T) {
 			},
 			want: EndpointTypeWS,
 		},
+		{
+			args: args{
+				URL: "ssh://example.com:22",
+				SSH: &SSH{
+					Username: "root",
+					Password: "password",
+				},
+			},
+			want: EndpointTypeSSH,
+		},
 		{
 			args: args{
 				URL: "invalid://example.org",
@@ -454,6 +465,52 @@ func TestEndpoint_ValidateAndSetDefaultsWithDNS(t *testing.T) {
 	}
 }
 
+func TestEndpoint_ValidateAndSetDefaultsWithSSH(t *testing.T) {
+	tests := []struct {
+		name        string
+		username    string
+		password    string
+		expectedErr error
+	}{
+		{
+			name:        "fail when has no user",
+			username:    "",
+			password:    "password",
+			expectedErr: ErrEndpointWithoutSSHUsername,
+		},
+		{
+			name:        "fail when has no password",
+			username:    "username",
+			password:    "",
+			expectedErr: ErrEndpointWithoutSSHPassword,
+		},
+		{
+			name:        "success when all fields are set",
+			username:    "username",
+			password:    "password",
+			expectedErr: nil,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			endpoint := &Endpoint{
+				Name: "ssh-test",
+				URL:  "https://example.com",
+				SSH: &SSH{
+					Username: test.username,
+					Password: test.password,
+				},
+				Conditions: []Condition{Condition("[STATUS] == 0")},
+			}
+			err := endpoint.ValidateAndSetDefaults()
+			if err != test.expectedErr {
+				t.Errorf("expected error %v, got %v", test.expectedErr, err)
+			}
+		})
+	}
+}
+
 func TestEndpoint_ValidateAndSetDefaultsWithSimpleErrors(t *testing.T) {
 	scenarios := []struct {
 		endpoint    *Endpoint
@@ -680,6 +737,55 @@ func TestIntegrationEvaluateHealthForDNS(t *testing.T) {
 	}
 }
 
+func TestIntegrationEvaluateHealthForSSH(t *testing.T) {
+	tests := []struct {
+		name       string
+		endpoint   Endpoint
+		conditions []Condition
+		success    bool
+	}{
+		{
+			name: "ssh-success",
+			endpoint: Endpoint{
+				Name: "ssh-success",
+				URL:  "ssh://localhost",
+				SSH: &SSH{
+					Username: "test",
+					Password: "test",
+				},
+				Body: "{ \"command\": \"uptime\" }",
+			},
+			conditions: []Condition{Condition("[STATUS] == 0")},
+			success:    true,
+		},
+		{
+			name: "ssh-failure",
+			endpoint: Endpoint{
+				Name: "ssh-failure",
+				URL:  "ssh://localhost",
+				SSH: &SSH{
+					Username: "test",
+					Password: "test",
+				},
+				Body: "{ \"command\": \"uptime\" }",
+			},
+			conditions: []Condition{Condition("[STATUS] == 1")},
+			success:    false,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			test.endpoint.ValidateAndSetDefaults()
+			test.endpoint.Conditions = test.conditions
+			result := test.endpoint.EvaluateHealth()
+			if result.Success != test.success {
+				t.Errorf("Expected success to be %v, but was %v", test.success, result.Success)
+			}
+		})
+	}
+}
+
 func TestIntegrationEvaluateHealthForICMP(t *testing.T) {
 	endpoint := Endpoint{
 		Name:       "icmp-test",