feat: Feature flag for relational tables (#10599)

# Which Problems Are Solved

This PR introduces a new feature flag `EnableRelationalTables` that will
be used in following implementations to decide whether Zitadel should
use the relational model or the event sourcing one.

# TODO

  - [x] Implement flag at system level
- [x] Display the flag on console:
https://github.com/zitadel/zitadel/pull/10615

# How the Problems Are Solved

  - Implement loading the flag from config
- Add persistence of the flag through gRPC endpoint
(SetInstanceFeatures)
- Implement reading of the flag through gRPC endpoint
(GetInstanceFeatures)

# Additional Changes

Some minor refactoring to remove un-needed generics annotations

# Additional Context

- Closes #10574

---------

Co-authored-by: Silvan <27845747+adlerhurst@users.noreply.github.com>

internal/command/instance_test.go

@@ -3,12 +3,15 @@ package command
 import (
 	"context"
 	"encoding/json"
+	"net/url"
 	"slices"
 	"strings"
 	"testing"
 	"time"
 
+	"github.com/muhlemmer/gu"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 	"go.uber.org/mock/gomock"
 	"golang.org/x/text/language"
 
@@ -18,6 +21,7 @@ import (
 	"github.com/zitadel/zitadel/internal/crypto"
 	"github.com/zitadel/zitadel/internal/domain"
 	"github.com/zitadel/zitadel/internal/eventstore"
+	"github.com/zitadel/zitadel/internal/feature"
 	"github.com/zitadel/zitadel/internal/id"
 	id_mock "github.com/zitadel/zitadel/internal/id/mock"
 	"github.com/zitadel/zitadel/internal/repository/instance"
@@ -1727,3 +1731,126 @@ func TestCommandSide_RemoveInstance(t *testing.T) {
 		})
 	}
 }
+
+func TestInstanceSetupFeatures_ToInstanceFeatures(t *testing.T) {
+	t.Parallel()
+
+	type fields struct {
+		LoginDefaultOrg                *bool
+		UserSchema                     *bool
+		TokenExchange                  *bool
+		ImprovedPerformance            []feature.ImprovedPerformanceType
+		DebugOIDCParentError           *bool
+		OIDCSingleV1SessionTermination *bool
+		EnableBackChannelLogout        *bool
+		LoginV2                        *InstanceSetupFeatureLoginV2
+		PermissionCheckV2              *bool
+		ConsoleUseV2UserApi            *bool
+		EnableRelationalTables         *bool
+	}
+
+	correctlyParsedURI, err := url.Parse("https://example.com")
+	require.NoError(t, err)
+
+	tt := []struct {
+		name    string
+		fields  fields
+		want    *InstanceFeatures
+		wantErr bool
+	}{
+		{
+			name:   "nil features returns nil",
+			fields: fields{},
+			want:   &InstanceFeatures{},
+		},
+		{
+			name: "all fields no login v2",
+			fields: fields{
+				LoginDefaultOrg:                gu.Ptr(true),
+				UserSchema:                     gu.Ptr(false),
+				TokenExchange:                  gu.Ptr(true),
+				ImprovedPerformance:            []feature.ImprovedPerformanceType{feature.ImprovedPerformanceTypeOrgDomainVerified},
+				DebugOIDCParentError:           gu.Ptr(true),
+				OIDCSingleV1SessionTermination: gu.Ptr(false),
+				EnableBackChannelLogout:        gu.Ptr(true),
+				PermissionCheckV2:              gu.Ptr(true),
+				ConsoleUseV2UserApi:            gu.Ptr(false),
+				EnableRelationalTables:         gu.Ptr(true),
+			},
+			want: &InstanceFeatures{
+				LoginDefaultOrg:                gu.Ptr(true),
+				UserSchema:                     gu.Ptr(false),
+				TokenExchange:                  gu.Ptr(true),
+				ImprovedPerformance:            []feature.ImprovedPerformanceType{feature.ImprovedPerformanceTypeOrgDomainVerified},
+				DebugOIDCParentError:           gu.Ptr(true),
+				OIDCSingleV1SessionTermination: gu.Ptr(false),
+				EnableBackChannelLogout:        gu.Ptr(true),
+				LoginV2:                        nil,
+				PermissionCheckV2:              gu.Ptr(true),
+				ConsoleUseV2UserApi:            gu.Ptr(false),
+				EnableRelationalTables:         gu.Ptr(true),
+			},
+		},
+		{
+			name: "with login v2 no base uri",
+			fields: fields{
+				LoginV2: &InstanceSetupFeatureLoginV2{
+					Required: true,
+				},
+			},
+			want: &InstanceFeatures{
+				LoginV2: &feature.LoginV2{
+					Required: true,
+				},
+			},
+		},
+		{
+			name: "with login v2 valid base uri",
+			fields: fields{
+				LoginV2: &InstanceSetupFeatureLoginV2{
+					Required: true,
+					BaseURI:  gu.Ptr("https://example.com"),
+				},
+			},
+			want: &InstanceFeatures{
+				LoginV2: &feature.LoginV2{
+					Required: true,
+					BaseURI:  correctlyParsedURI,
+				},
+			},
+		},
+		{
+			name: "with login v2 invalid base uri",
+			fields: fields{
+				LoginV2: &InstanceSetupFeatureLoginV2{
+					Required: true,
+					BaseURI:  gu.Ptr("://invalid"),
+				},
+			},
+			wantErr: true,
+		},
+	}
+	for _, tc := range tt {
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+
+			f := &InstanceSetupFeatures{
+				LoginDefaultOrg:                tc.fields.LoginDefaultOrg,
+				UserSchema:                     tc.fields.UserSchema,
+				TokenExchange:                  tc.fields.TokenExchange,
+				ImprovedPerformance:            tc.fields.ImprovedPerformance,
+				DebugOIDCParentError:           tc.fields.DebugOIDCParentError,
+				OIDCSingleV1SessionTermination: tc.fields.OIDCSingleV1SessionTermination,
+				EnableBackChannelLogout:        tc.fields.EnableBackChannelLogout,
+				LoginV2:                        tc.fields.LoginV2,
+				PermissionCheckV2:              tc.fields.PermissionCheckV2,
+				ConsoleUseV2UserApi:            tc.fields.ConsoleUseV2UserApi,
+				EnableRelationalTables:         tc.fields.EnableRelationalTables,
+			}
+			got, err := f.ToInstanceFeatures()
+
+			require.Equal(t, tc.wantErr, err != nil)
+			assert.Equal(t, tc.want, got)
+		})
+	}
+}