feat: create user scim v2 endpoint (#9132)

# Which Problems Are Solved
- Adds infrastructure code (basic implementation, error handling,
middlewares, ...) to implement the SCIM v2 interface
- Adds support for the user create SCIM v2 endpoint

# How the Problems Are Solved
- Adds support for the user create SCIM v2 endpoint under `POST
/scim/v2/{orgID}/Users`

# Additional Context

Part of #8140

internal/api/scim/schemas/string_test.go

@@ -0,0 +1,70 @@
+package schemas
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestWriteOnlyString_MarshalJSON(t *testing.T) {
+	tests := []struct {
+		name string
+		s    WriteOnlyString
+	}{
+		{
+			name: "always returns null",
+			s:    "foo bar",
+		},
+		{
+			name: "empty string returns null",
+			s:    "",
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got, err := json.Marshal(&tt.s)
+			assert.NoError(t, err)
+			assert.Equal(t, "null", string(got))
+		})
+	}
+}
+
+func TestWriteOnlyString_UnmarshalJSON(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   []byte
+		want    WriteOnlyString
+		wantErr bool
+	}{
+		{
+			name:    "string",
+			input:   []byte(`"fooBar"`),
+			want:    "fooBar",
+			wantErr: false,
+		},
+		{
+			name:    "empty string",
+			input:   []byte(`""`),
+			want:    "",
+			wantErr: false,
+		},
+		{
+			name:    "bad format",
+			input:   []byte(`"bad "format"`),
+			want:    "",
+			wantErr: true,
+		},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var got WriteOnlyString
+			err := json.Unmarshal(tt.input, &got)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("UnmarshalJSON() error = %v, wantErr %v", err, tt.wantErr)
+			}
+
+			assert.Equal(t, tt.want, got)
+		})
+	}
+}